source: draft-ietf-httpbis/02/draft-ietf-httpbis-p1-messaging-02.xml @ 2111

Last change on this file since 2111 was 1500, checked in by julian.reschke@…, 10 years ago

fix mime types

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  • Property svn:mime-type set to text/xml
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1<?xml version="1.0" encoding="UTF-8"?>
3    This XML document is the output of clean-for-DTD.xslt; a tool that strips
4    extensions to RFC2629(bis) from documents for processing with xml2rfc.
6<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
7<?rfc toc="yes" ?>
8<?rfc symrefs="yes" ?>
9<?rfc sortrefs="yes" ?>
10<?rfc compact="yes"?>
11<?rfc subcompact="no" ?>
12<?rfc linkmailto="no" ?>
13<?rfc editing="no" ?>
14<?rfc comments="yes"?>
15<?rfc inline="yes"?>
16<!DOCTYPE rfc
17  PUBLIC "" "rfc2629.dtd">
18<rfc obsoletes="2616" category="std" ipr="full3978" docName="draft-ietf-httpbis-p1-messaging-02">
21  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
23  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
24    <organization abbrev="Day Software">Day Software</organization>
25    <address>
26      <postal>
27        <street>23 Corporate Plaza DR, Suite 280</street>
28        <city>Newport Beach</city>
29        <region>CA</region>
30        <code>92660</code>
31        <country>USA</country>
32      </postal>
33      <phone>+1-949-706-5300</phone>
34      <facsimile>+1-949-706-5305</facsimile>
35      <email></email>
36      <uri></uri>
37    </address>
38  </author>
40  <author initials="J." surname="Gettys" fullname="Jim Gettys">
41    <organization>One Laptop per Child</organization>
42    <address>
43      <postal>
44        <street>21 Oak Knoll Road</street>
45        <city>Carlisle</city>
46        <region>MA</region>
47        <code>01741</code>
48        <country>USA</country>
49      </postal>
50      <email></email>
51      <uri></uri>
52    </address>
53  </author>
55  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
56    <organization abbrev="HP">Hewlett-Packard Company</organization>
57    <address>
58      <postal>
59        <street>HP Labs, Large Scale Systems Group</street>
60        <street>1501 Page Mill Road, MS 1177</street>
61        <city>Palo Alto</city>
62        <region>CA</region>
63        <code>94304</code>
64        <country>USA</country>
65      </postal>
66      <email></email>
67    </address>
68  </author>
70  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
71    <organization abbrev="Microsoft">Microsoft Corporation</organization>
72    <address>
73      <postal>
74        <street>1 Microsoft Way</street>
75        <city>Redmond</city>
76        <region>WA</region>
77        <code>98052</code>
78        <country>USA</country>
79      </postal>
80      <email></email>
81    </address>
82  </author>
84  <author initials="L." surname="Masinter" fullname="Larry Masinter">
85    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
86    <address>
87      <postal>
88        <street>345 Park Ave</street>
89        <city>San Jose</city>
90        <region>CA</region>
91        <code>95110</code>
92        <country>USA</country>
93      </postal>
94      <email></email>
95      <uri></uri>
96    </address>
97  </author>
99  <author initials="P." surname="Leach" fullname="Paul J. Leach">
100    <organization abbrev="Microsoft">Microsoft Corporation</organization>
101    <address>
102      <postal>
103        <street>1 Microsoft Way</street>
104        <city>Redmond</city>
105        <region>WA</region>
106        <code>98052</code>
107      </postal>
108      <email></email>
109    </address>
110  </author>
112  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
113    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
114    <address>
115      <postal>
116        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
117        <street>The Stata Center, Building 32</street>
118        <street>32 Vassar Street</street>
119        <city>Cambridge</city>
120        <region>MA</region>
121        <code>02139</code>
122        <country>USA</country>
123      </postal>
124      <email></email>
125      <uri></uri>
126    </address>
127  </author>
129  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
130    <organization abbrev="W3C">World Wide Web Consortium</organization>
131    <address>
132      <postal>
133        <street>W3C / ERCIM</street>
134        <street>2004, rte des Lucioles</street>
135        <city>Sophia-Antipolis</city>
136        <region>AM</region>
137        <code>06902</code>
138        <country>France</country>
139      </postal>
140      <email></email>
141      <uri></uri>
142    </address>
143  </author>
145  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
146    <organization abbrev="greenbytes">greenbytes GmbH</organization>
147    <address>
148      <postal>
149        <street>Hafenweg 16</street>
150        <city>Muenster</city><region>NW</region><code>48155</code>
151        <country>Germany</country>
152      </postal>
153      <phone>+49 251 2807760</phone>   
154      <facsimile>+49 251 2807761</facsimile>   
155      <email></email>       
156      <uri></uri>     
157    </address>
158  </author>
160  <date month="February" year="2008" day="24"/>
164   The Hypertext Transfer Protocol (HTTP) is an application-level
165   protocol for distributed, collaborative, hypermedia information
166   systems. HTTP has been in use by the World Wide Web global information
167   initiative since 1990. This document is Part 1 of the seven-part specification
168   that defines the protocol referred to as "HTTP/1.1" and, taken together,
169   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
170   its associated terminology, defines the "http" and "https" Uniform
171   Resource Identifier (URI) schemes, defines the generic message syntax
172   and parsing requirements for HTTP message frames, and describes
173   general security concerns for implementations.
177<note title="Editorial Note (To be removed by RFC Editor)">
178  <t>
179    Discussion of this draft should take place on the HTTPBIS working group
180    mailing list ( The current issues list is
181    at <eref target=""/>
182    and related documents (including fancy diffs) can be found at
183    <eref target=""/>.
184  </t>
185  <t>
186    This draft incorporates those issue resolutions that were either
187    collected in the original RFC2616 errata list (<eref target=""/>),
188    or which were agreed upon on the mailing list between October 2006 and
189    November 2007 (as published in "draft-lafon-rfc2616bis-03").
190  </t>
194<section title="Introduction" anchor="introduction">
196   The Hypertext Transfer Protocol (HTTP) is an application-level
197   protocol for distributed, collaborative, hypermedia information
198   systems. HTTP has been in use by the World-Wide Web global
199   information initiative since 1990. The first version of HTTP, commonly
200   referred to as HTTP/0.9, was a simple protocol for raw data transfer
201   across the Internet with only a single method and no metadata.
202   HTTP/1.0, as defined by <xref target="RFC1945"/>, improved
203   the protocol by allowing messages to be in the format of MIME-like
204   messages, containing metadata about the data transferred and
205   modifiers on the request/response semantics. However, HTTP/1.0 did
206   not sufficiently take into consideration the effects of hierarchical
207   proxies, caching, the need for persistent connections, or name-based
208   virtual hosts. In addition, the proliferation of incompletely-implemented
209   applications calling themselves "HTTP/1.0" necessitated a
210   protocol version change in order for two communicating applications
211   to determine each other's true capabilities.
214   This document is Part 1 of the seven-part specification that defines
215   the protocol referred to as "HTTP/1.1", obsoleting <xref target="RFC2616"/>.
216   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
217   requirements that enable reliable implementations and adding only
218   those new features that will either be safely ignored by an HTTP/1.0
219   recipient or only sent when communicating with a party advertising
220   compliance with HTTP/1.1.
221   Part 1 defines those aspects of HTTP/1.1 related to overall network
222   operation, message framing, interaction with transport protocols, and
223   URI schemes.
226   This document is currently disorganized in order to minimize the changes
227   between drafts and enable reviewers to see the smaller errata changes.
228   The next draft will reorganize the sections to better reflect the content.
229   In particular, the sections will be organized according to the typical
230   process of deciding when to use HTTP (URI schemes), overall network operation,
231   connection management, message framing, and generic message parsing.
232   The current mess reflects how widely dispersed these topics and associated
233   requirements had become in <xref target="RFC2616"/>.
236<section title="Purpose" anchor="intro.purpose">
238   Practical information systems require more functionality than simple
239   retrieval, including search, front-end update, and annotation. HTTP
240   allows an open-ended set of methods and headers that indicate the
241   purpose of a request <xref target="RFC2324"/>. It builds on the discipline of reference
242   provided by the Uniform Resource Identifier (URI) <xref target="RFC1630"/>, as a location
243   (URL) <xref target="RFC1738"/> or name (URN) <xref target="RFC1737"/>, for indicating the resource to which a
244   method is to be applied. Messages are passed in a format similar to
245   that used by Internet mail <xref target="RFC2822"/> as defined by the Multipurpose
246   Internet Mail Extensions (MIME) <xref target="RFC2045"/>.
249   HTTP is also used as a generic protocol for communication between
250   user agents and proxies/gateways to other Internet systems, including
251   those supported by the SMTP <xref target="RFC2821"/>, NNTP <xref target="RFC3977"/>, FTP <xref target="RFC959"/>, Gopher <xref target="RFC1436"/>,
252   and WAIS <xref target="WAIS"/> protocols. In this way, HTTP allows basic hypermedia
253   access to resources available from diverse applications.
257<section title="Requirements" anchor="intro.requirements">
259   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
260   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
261   document are to be interpreted as described in <xref target="RFC2119"/>.
264   An implementation is not compliant if it fails to satisfy one or more
265   of the MUST or REQUIRED level requirements for the protocols it
266   implements. An implementation that satisfies all the MUST or REQUIRED
267   level and all the SHOULD level requirements for its protocols is said
268   to be "unconditionally compliant"; one that satisfies all the MUST
269   level requirements but not all the SHOULD level requirements for its
270   protocols is said to be "conditionally compliant."
274<section title="Terminology" anchor="intro.terminology">
276   This specification uses a number of terms to refer to the roles
277   played by participants in, and objects of, the HTTP communication.
280  <iref item="connection"/>
281  connection
282  <list>
283    <t>
284      A transport layer virtual circuit established between two programs
285      for the purpose of communication.
286    </t>
287  </list>
290  <iref item="message"/>
291  message
292  <list>
293    <t>
294      The basic unit of HTTP communication, consisting of a structured
295      sequence of octets matching the syntax defined in <xref target="http.message"/> and
296      transmitted via the connection.
297    </t>
298  </list>
301  <iref item="request"/>
302  request
303  <list>
304    <t>
305      An HTTP request message, as defined in <xref target="request"/>.
306    </t>
307  </list>
310  <iref item="response"/>
311  response
312  <list>
313    <t>
314      An HTTP response message, as defined in <xref target="response"/>.
315    </t>
316  </list>
319  <iref item="resource"/>
320  resource
321  <list>
322    <t>
323      A network data object or service that can be identified by a URI,
324      as defined in <xref target="uri"/>. Resources may be available in multiple
325      representations (e.g. multiple languages, data formats, size, and
326      resolutions) or vary in other ways.
327    </t>
328  </list>
331  <iref item="entity"/>
332  entity
333  <list>
334    <t>
335      The information transferred as the payload of a request or
336      response. An entity consists of metainformation in the form of
337      entity-header fields and content in the form of an entity-body, as
338      described in Section 4 of <xref target="Part3"/>.
339    </t>
340  </list>
343  <iref item="representation"/>
344  representation
345  <list>
346    <t>
347      An entity included with a response that is subject to content
348      negotiation, as described in Section 5 of <xref target="Part3"/>. There may exist multiple
349      representations associated with a particular response status.
350    </t>
351  </list>
354  <iref item="content negotiation"/>
355  content negotiation
356  <list>
357    <t>
358      The mechanism for selecting the appropriate representation when
359      servicing a request, as described in Section 5 of <xref target="Part3"/>. The
360      representation of entities in any response can be negotiated
361      (including error responses).
362    </t>
363  </list>
366  <iref item="variant"/>
367  variant
368  <list>
369    <t>
370      A resource may have one, or more than one, representation(s)
371      associated with it at any given instant. Each of these
372      representations is termed a `variant'.  Use of the term `variant'
373      does not necessarily imply that the resource is subject to content
374      negotiation.
375    </t>
376  </list>
379  <iref item="client"/>
380  client
381  <list>
382    <t>
383      A program that establishes connections for the purpose of sending
384      requests.
385    </t>
386  </list>
389  <iref item="user agent"/>
390  user agent
391  <list>
392    <t>
393      The client which initiates a request. These are often browsers,
394      editors, spiders (web-traversing robots), or other end user tools.
395    </t>
396  </list>
399  <iref item="server"/>
400  server
401  <list>
402    <t>
403      An application program that accepts connections in order to
404      service requests by sending back responses. Any given program may
405      be capable of being both a client and a server; our use of these
406      terms refers only to the role being performed by the program for a
407      particular connection, rather than to the program's capabilities
408      in general. Likewise, any server may act as an origin server,
409      proxy, gateway, or tunnel, switching behavior based on the nature
410      of each request.
411    </t>
412  </list>
415  <iref item="origin server"/>
416  origin server
417  <list>
418    <t>
419      The server on which a given resource resides or is to be created.
420    </t>
421  </list>
424  <iref item="proxy"/>
425  proxy
426  <list>
427    <t>
428      An intermediary program which acts as both a server and a client
429      for the purpose of making requests on behalf of other clients.
430      Requests are serviced internally or by passing them on, with
431      possible translation, to other servers. A proxy MUST implement
432      both the client and server requirements of this specification. A
433      "transparent proxy" is a proxy that does not modify the request or
434      response beyond what is required for proxy authentication and
435      identification. A "non-transparent proxy" is a proxy that modifies
436      the request or response in order to provide some added service to
437      the user agent, such as group annotation services, media type
438      transformation, protocol reduction, or anonymity filtering. Except
439      where either transparent or non-transparent behavior is explicitly
440      stated, the HTTP proxy requirements apply to both types of
441      proxies.
442    </t>
443  </list>
446  <iref item="gateway"/>
447  gateway
448  <list>
449    <t>
450      A server which acts as an intermediary for some other server.
451      Unlike a proxy, a gateway receives requests as if it were the
452      origin server for the requested resource; the requesting client
453      may not be aware that it is communicating with a gateway.
454    </t>
455  </list>
458  <iref item="tunnel"/>
459  tunnel
460  <list>
461    <t>
462      An intermediary program which is acting as a blind relay between
463      two connections. Once active, a tunnel is not considered a party
464      to the HTTP communication, though the tunnel may have been
465      initiated by an HTTP request. The tunnel ceases to exist when both
466      ends of the relayed connections are closed.
467    </t>
468  </list>
471  <iref item="cache"/>
472  cache
473  <list>
474    <t>
475      A program's local store of response messages and the subsystem
476      that controls its message storage, retrieval, and deletion. A
477      cache stores cacheable responses in order to reduce the response
478      time and network bandwidth consumption on future, equivalent
479      requests. Any client or server may include a cache, though a cache
480      cannot be used by a server that is acting as a tunnel.
481    </t>
482  </list>
485  <iref item="cacheable"/>
486  cacheable
487  <list>
488    <t>
489      A response is cacheable if a cache is allowed to store a copy of
490      the response message for use in answering subsequent requests. The
491      rules for determining the cacheability of HTTP responses are
492      defined in Section 1 of <xref target="Part6"/>. Even if a resource is cacheable, there may
493      be additional constraints on whether a cache can use the cached
494      copy for a particular request.
495    </t>
496  </list>
499  <iref item="upstream"/>
500  <iref item="downstream"/>
501  upstream/downstream
502  <list>
503    <t>
504      Upstream and downstream describe the flow of a message: all
505      messages flow from upstream to downstream.
506    </t>
507  </list>
510  <iref item="inbound"/>
511  <iref item="outbound"/>
512  inbound/outbound
513  <list>
514    <t>
515      Inbound and outbound refer to the request and response paths for
516      messages: "inbound" means "traveling toward the origin server",
517      and "outbound" means "traveling toward the user agent"
518    </t>
519  </list>
523<section title="Overall Operation" anchor="intro.overall.operation">
525   HTTP is a request/response protocol. A client sends a
526   request to the server in the form of a request method, URI, and
527   protocol version, followed by a MIME-like message containing request
528   modifiers, client information, and possible body content over a
529   connection with a server. The server responds with a status line,
530   including the message's protocol version and a success or error code,
531   followed by a MIME-like message containing server information, entity
532   metainformation, and possible entity-body content. The relationship
533   between HTTP and MIME is described in Appendix A of <xref target="Part3"/>.
536   Most HTTP communication is initiated by a user agent and consists of
537   a request to be applied to a resource on some origin server. In the
538   simplest case, this may be accomplished via a single connection (v)
539   between the user agent (UA) and the origin server (O).
541<figure><artwork type="drawing"><![CDATA[
542       request chain ------------------------>
543    UA -------------------v------------------- O
544       <----------------------- response chain
547   A more complicated situation occurs when one or more intermediaries
548   are present in the request/response chain. There are three common
549   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
550   forwarding agent, receiving requests for a URI in its absolute form,
551   rewriting all or part of the message, and forwarding the reformatted
552   request toward the server identified by the URI. A gateway is a
553   receiving agent, acting as a layer above some other server(s) and, if
554   necessary, translating the requests to the underlying server's
555   protocol. A tunnel acts as a relay point between two connections
556   without changing the messages; tunnels are used when the
557   communication needs to pass through an intermediary (such as a
558   firewall) even when the intermediary cannot understand the contents
559   of the messages.
561<figure><artwork type="drawing"><![CDATA[
562       request chain -------------------------------------->
563    UA -----v----- A -----v----- B -----v----- C -----v----- O
564       <------------------------------------- response chain
567   The figure above shows three intermediaries (A, B, and C) between the
568   user agent and origin server. A request or response message that
569   travels the whole chain will pass through four separate connections.
570   This distinction is important because some HTTP communication options
571   may apply only to the connection with the nearest, non-tunnel
572   neighbor, only to the end-points of the chain, or to all connections
573   along the chain. Although the diagram is linear, each participant may
574   be engaged in multiple, simultaneous communications. For example, B
575   may be receiving requests from many clients other than A, and/or
576   forwarding requests to servers other than C, at the same time that it
577   is handling A's request.
580   Any party to the communication which is not acting as a tunnel may
581   employ an internal cache for handling requests. The effect of a cache
582   is that the request/response chain is shortened if one of the
583   participants along the chain has a cached response applicable to that
584   request. The following illustrates the resulting chain if B has a
585   cached copy of an earlier response from O (via C) for a request which
586   has not been cached by UA or A.
588<figure><artwork type="drawing"><![CDATA[
589          request chain ---------->
590       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
591          <--------- response chain
594   Not all responses are usefully cacheable, and some requests may
595   contain modifiers which place special requirements on cache behavior.
596   HTTP requirements for cache behavior and cacheable responses are
597   defined in Section 1 of <xref target="Part6"/>.
600   In fact, there are a wide variety of architectures and configurations
601   of caches and proxies currently being experimented with or deployed
602   across the World Wide Web. These systems include national hierarchies
603   of proxy caches to save transoceanic bandwidth, systems that
604   broadcast or multicast cache entries, organizations that distribute
605   subsets of cached data via CD-ROM, and so on. HTTP systems are used
606   in corporate intranets over high-bandwidth links, and for access via
607   PDAs with low-power radio links and intermittent connectivity. The
608   goal of HTTP/1.1 is to support the wide diversity of configurations
609   already deployed while introducing protocol constructs that meet the
610   needs of those who build web applications that require high
611   reliability and, failing that, at least reliable indications of
612   failure.
615   HTTP communication usually takes place over TCP/IP connections. The
616   default port is TCP 80 (<eref target=""/>), but other ports can be used. This does
617   not preclude HTTP from being implemented on top of any other protocol
618   on the Internet, or on other networks. HTTP only presumes a reliable
619   transport; any protocol that provides such guarantees can be used;
620   the mapping of the HTTP/1.1 request and response structures onto the
621   transport data units of the protocol in question is outside the scope
622   of this specification.
625   In HTTP/1.0, most implementations used a new connection for each
626   request/response exchange. In HTTP/1.1, a connection may be used for
627   one or more request/response exchanges, although connections may be
628   closed for a variety of reasons (see <xref target="persistent.connections"/>).
633<section title="Notational Conventions and Generic Grammar" anchor="notation">
635<section title="Augmented BNF" anchor="notation.abnf">
637   All of the mechanisms specified in this document are described in
638   both prose and an augmented Backus-Naur Form (BNF) similar to that
639   used by <xref target="RFC822ABNF"/>. Implementors will need to be familiar with the
640   notation in order to understand this specification. The augmented BNF
641   includes the following constructs:
644   name = definition
645  <list>
646    <t>
647      The name of a rule is simply the name itself (without any
648      enclosing "&lt;" and "&gt;") and is separated from its definition by the
649      equal "=" character. White space is only significant in that
650      indentation of continuation lines is used to indicate a rule
651      definition that spans more than one line. Certain basic rules are
652      in uppercase, such as SP, LWS, HTAB, CRLF, DIGIT, ALPHA, etc. Angle
653      brackets are used within definitions whenever their presence will
654      facilitate discerning the use of rule names.
655    </t>
656  </list>
659   "literal"
660  <list>
661    <t>
662      Quotation marks surround literal text. Unless stated otherwise,
663      the text is case-insensitive.
664    </t>
665  </list>
668   rule1 | rule2
669  <list>
670    <t>
671      Elements separated by a bar ("|") are alternatives, e.g., "yes |
672      no" will accept yes or no.
673    </t>
674  </list>
677   (rule1 rule2)
678  <list>
679    <t>
680      Elements enclosed in parentheses are treated as a single element.
681      Thus, "(elem (foo | bar) elem)" allows the token sequences "elem
682      foo elem" and "elem bar elem".
683    </t>
684  </list>
687   *rule
688  <list>
689    <t>
690      The character "*" preceding an element indicates repetition. The
691      full form is "&lt;n&gt;*&lt;m&gt;element" indicating at least &lt;n&gt; and at most
692      &lt;m&gt; occurrences of element. Default values are 0 and infinity so
693      that "*(element)" allows any number, including zero; "1*element"
694      requires at least one; and "1*2element" allows one or two.
695    </t>
696  </list>
699   [rule]
700  <list>
701    <t>
702      Square brackets enclose optional elements; "[foo bar]" is
703      equivalent to "*1(foo bar)".
704    </t>
705  </list>
708   N rule
709  <list>
710    <t>
711      Specific repetition: "&lt;n&gt;(element)" is equivalent to
712      "&lt;n&gt;*&lt;n&gt;(element)"; that is, exactly &lt;n&gt; occurrences of (element).
713      Thus 2DIGIT is a 2-digit number, and 3ALPHA is a string of three
714      alphabetic characters.
715    </t>
716  </list>
719   #rule
720  <list>
721    <t>
722      A construct "#" is defined, similar to "*", for defining lists of
723      elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
724      &lt;n&gt; and at most &lt;m&gt; elements, each separated by one or more commas
725      (",") and OPTIONAL linear white space (LWS). This makes the usual
726      form of lists very easy; a rule such as
727    </t>
728    <t>
729         ( *LWS element *( *LWS "," *LWS element ))
730    </t>
731    <t>
732      can be shown as
733    </t>
734    <t>
735         1#element
736    </t>
737    <t>
738      Wherever this construct is used, null elements are allowed, but do
739      not contribute to the count of elements present. That is,
740      "(element), , (element) " is permitted, but counts as only two
741      elements. Therefore, where at least one element is required, at
742      least one non-null element MUST be present. Default values are 0
743      and infinity so that "#element" allows any number, including zero;
744      "1#element" requires at least one; and "1#2element" allows one or
745      two.
746    </t>
747  </list>
750   ; comment
751  <list>
752    <t>
753      A semi-colon, set off some distance to the right of rule text,
754      starts a comment that continues to the end of line. This is a
755      simple way of including useful notes in parallel with the
756      specifications.
757    </t>
758  </list>
761   implied *LWS
762  <list>
763    <t>
764      The grammar described by this specification is word-based. Except
765      where noted otherwise, linear white space (LWS) can be included
766      between any two adjacent words (token or quoted-string), and
767      between adjacent words and separators, without changing the
768      interpretation of a field. At least one delimiter (LWS and/or
769      separators) MUST exist between any two tokens (for the definition
770      of "token" below), since they would otherwise be interpreted as a
771      single token.
772    </t>
773  </list>
777<section title="Basic Rules" anchor="basic.rules">
799   The following rules are used throughout this specification to
800   describe basic parsing constructs. The US-ASCII coded character set
801   is defined by ANSI X3.4-1986 <xref target="USASCII"/>.
803<figure><iref primary="true" item="Grammar" subitem="OCTET"/><iref primary="true" item="Grammar" subitem="CHAR"/><iref primary="true" item="Grammar" subitem="ALPHA"/><iref primary="true" item="Grammar" subitem="DIGIT"/><iref primary="true" item="Grammar" subitem="CTL"/><iref primary="true" item="Grammar" subitem="CR"/><iref primary="true" item="Grammar" subitem="LF"/><iref primary="true" item="Grammar" subitem="SP"/><iref primary="true" item="Grammar" subitem="HTAB"/><iref primary="true" item="Grammar" subitem="DQUOTE"/><artwork type="abnf2616"><![CDATA[
804  OCTET          = %x00-FF
805                   ; any 8-bit sequence of data
806  CHAR           = %x01-7F
807                   ; any US-ASCII character, excluding NUL
808  ALPHA          = %x41-5A | %x61-7A
809                   ; A-Z | a-z
810  DIGIT          = %x30-39
811                   ; any US-ASCII digit "0".."9"
812  CTL            = %x00-1F | %x7F
813                   ; (octets 0 - 31) and DEL (127)
814  CR             = %x0D
815                   ; US-ASCII CR, carriage return (13)
816  LF             = %x0A
817                   ; US-ASCII LF, linefeed (10)
818  SP             = %x20
819                   ; US-ASCII SP, space (32)
820  HTAB           = %x09
821                   ; US-ASCII HT, horizontal-tab (9)
822  DQUOTE         = %x22
823                   ; US-ASCII double-quote mark (34)
826   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
827   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
828   tolerant applications). The end-of-line marker within an entity-body
829   is defined by its associated media type, as described in Section 3.3 of <xref target="Part3"/>.
831<figure><iref primary="true" item="Grammar" subitem="CRLF"/><artwork type="abnf2616"><![CDATA[
832  CRLF           = CR LF
835   HTTP/1.1 header field values can be folded onto multiple lines if the
836   continuation line begins with a space or horizontal tab. All linear
837   white space, including folding, has the same semantics as SP. A
838   recipient MAY replace any linear white space with a single SP before
839   interpreting the field value or forwarding the message downstream.
841<figure><iref primary="true" item="Grammar" subitem="LWS"/><artwork type="abnf2616"><![CDATA[
842  LWS            = [CRLF] 1*( SP | HTAB )
845   The TEXT rule is only used for descriptive field contents and values
846   that are not intended to be interpreted by the message parser. Words
847   of *TEXT MAY contain characters from character sets other than ISO-8859-1
848   <xref target="ISO-8859-1"/> only when encoded according to the rules of
849   <xref target="RFC2047"/>.
851<figure><iref primary="true" item="Grammar" subitem="TEXT"/><artwork type="abnf2616"><![CDATA[
852  TEXT           = %x20-7E | %x80-FF | LWS
853                 ; any OCTET except CTLs, but including LWS
856   A CRLF is allowed in the definition of TEXT only as part of a header
857   field continuation. It is expected that the folding LWS will be
858   replaced with a single SP before interpretation of the TEXT value.
861   Hexadecimal numeric characters are used in several protocol elements.
863<figure><iref primary="true" item="Grammar" subitem="HEX"/><artwork type="abnf2616"><![CDATA[
864  HEX            = "A" | "B" | "C" | "D" | "E" | "F"
865                 | "a" | "b" | "c" | "d" | "e" | "f" | DIGIT
868   Many HTTP/1.1 header field values consist of words separated by LWS
869   or special characters. These special characters MUST be in a quoted
870   string to be used within a parameter value (as defined in
871   <xref target="transfer.codings"/>).
873<figure><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="separators"/><artwork type="abnf2616"><![CDATA[
874  separators     = "(" | ")" | "<" | ">" | "@"
875                 | "," | ";" | ":" | "\" | DQUOTE
876                 | "/" | "[" | "]" | "?" | "="
877                 | "{" | "}" | SP | HTAB
879  tchar          = "!" | "#" | "$" | "%" | "&" | "'" | "*"
880                 | "+" | "-" | "." | "^" | "_" | "`" | "|" | "~"
881                 | DIGIT | ALPHA
882                 ; any CHAR except CTLs or separators
884  token          = 1*tchar
887   Comments can be included in some HTTP header fields by surrounding
888   the comment text with parentheses. Comments are only allowed in
889   fields containing "comment" as part of their field value definition.
890   In all other fields, parentheses are considered part of the field
891   value.
893<figure><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/><artwork type="abnf2616"><![CDATA[
894  comment        = "(" *( ctext | quoted-pair | comment ) ")"
895  ctext          = <any TEXT excluding "(" and ")">
898   A string of text is parsed as a single word if it is quoted using
899   double-quote marks.
901<figure><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/><artwork type="abnf2616"><![CDATA[
902  quoted-string  = ( DQUOTE *(qdtext | quoted-pair ) DQUOTE )
903  qdtext         = <any TEXT excluding DQUOTE and "\">
906   The backslash character ("\") MAY be used as a single-character
907   quoting mechanism only within quoted-string and comment constructs.
909<figure><iref primary="true" item="Grammar" subitem="quoted-pair"/><artwork type="abnf2616"><![CDATA[
910  quoted-pair    = "\" CHAR
914<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
916  The ABNF rules below are defined in other parts:
918<figure><!-- Part2--><artwork type="abnf2616"><![CDATA[
919  request-header =  <request-header, defined in [Part2], Section 4>
920  response-header = <response-header, defined in [Part2], Section 6>
922<figure><!-- Part3--><artwork type="abnf2616"><![CDATA[
923  accept-params   = <accept-params, defined in [Part3], Section 6.1>
924  entity-body     = <entity-body, defined in [Part3], Section 4.2>
925  entity-header   = <entity-header, defined in [Part3], Section 4.1>
927<figure><!-- Part6--><artwork type="abnf2616"><![CDATA[
928  Cache-Control   = <Cache-Control, defined in [Part6], Section 16.4>
929  Pragma          = <Pragma, defined in [Part6], Section 16.4>
930  Warning         = <Warning, defined in [Part6], Section 16.6>
936<section title="Protocol Parameters" anchor="protocol.parameters">
938<section title="HTTP Version" anchor="http.version">
940   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
941   of the protocol. The protocol versioning policy is intended to allow
942   the sender to indicate the format of a message and its capacity for
943   understanding further HTTP communication, rather than the features
944   obtained via that communication. No change is made to the version
945   number for the addition of message components which do not affect
946   communication behavior or which only add to extensible field values.
947   The &lt;minor&gt; number is incremented when the changes made to the
948   protocol add features which do not change the general message parsing
949   algorithm, but which may add to the message semantics and imply
950   additional capabilities of the sender. The &lt;major&gt; number is
951   incremented when the format of a message within the protocol is
952   changed. See <xref target="RFC2145"/> for a fuller explanation.
955   The version of an HTTP message is indicated by an HTTP-Version field
956   in the first line of the message. HTTP-Version is case-sensitive.
958<figure><iref primary="true" item="Grammar" subitem="HTTP-Version"/><artwork type="abnf2616"><![CDATA[
959  HTTP-Version   = "HTTP" "/" 1*DIGIT "." 1*DIGIT
962   Note that the major and minor numbers MUST be treated as separate
963   integers and that each MAY be incremented higher than a single digit.
964   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
965   lower than HTTP/12.3. Leading zeros MUST be ignored by recipients and
966   MUST NOT be sent.
969   An application that sends a request or response message that includes
970   HTTP-Version of "HTTP/1.1" MUST be at least conditionally compliant
971   with this specification. Applications that are at least conditionally
972   compliant with this specification SHOULD use an HTTP-Version of
973   "HTTP/1.1" in their messages, and MUST do so for any message that is
974   not compatible with HTTP/1.0. For more details on when to send
975   specific HTTP-Version values, see <xref target="RFC2145"/>.
978   The HTTP version of an application is the highest HTTP version for
979   which the application is at least conditionally compliant.
982   Proxy and gateway applications need to be careful when forwarding
983   messages in protocol versions different from that of the application.
984   Since the protocol version indicates the protocol capability of the
985   sender, a proxy/gateway MUST NOT send a message with a version
986   indicator which is greater than its actual version. If a higher
987   version request is received, the proxy/gateway MUST either downgrade
988   the request version, or respond with an error, or switch to tunnel
989   behavior.
992   Due to interoperability problems with HTTP/1.0 proxies discovered
993   since the publication of <xref target="RFC2068"/>, caching proxies MUST, gateways
994   MAY, and tunnels MUST NOT upgrade the request to the highest version
995   they support. The proxy/gateway's response to that request MUST be in
996   the same major version as the request.
999  <list>
1000    <t>
1001      Note: Converting between versions of HTTP may involve modification
1002      of header fields required or forbidden by the versions involved.
1003    </t>
1004  </list>
1008<section title="Uniform Resource Identifiers" anchor="uri">
1010   URIs have been known by many names: WWW addresses, Universal Document
1011   Identifiers, Universal Resource Identifiers <xref target="RFC1630"/>, and finally the
1012   combination of Uniform Resource Locators (URL) <xref target="RFC1738"/> and Names (URN)
1013   <xref target="RFC1737"/>. As far as HTTP is concerned, Uniform Resource Identifiers are
1014   simply formatted strings which identify--via name, location, or any
1015   other characteristic--a resource.
1018<section title="General Syntax" anchor="general.syntax">
1020   URIs in HTTP can be represented in absolute form or relative to some
1021   known base URI <xref target="RFC1808"/>, depending upon the context of their use. The two
1022   forms are differentiated by the fact that absolute URIs always begin
1023   with a scheme name followed by a colon. For definitive information on
1024   URL syntax and semantics, see "Uniform Resource Identifiers (URI):
1025   Generic Syntax and Semantics," <xref target="RFC2396"/> (which replaces <xref target="RFC1738"/>
1026   and <xref target="RFC1808"/>). This specification adopts the
1027   definitions of "URI-reference", "absoluteURI", "fragment", "relativeURI", "port",
1028   "host", "abs_path", "query", and "authority" from that specification:
1030<figure><iref primary="true" item="Grammar" subitem="absoluteURI"/><iref primary="true" item="Grammar" subitem="authority"/><iref primary="true" item="Grammar" subitem="path-absolute"/><iref primary="true" item="Grammar" subitem="port"/><iref primary="true" item="Grammar" subitem="query"/><iref primary="true" item="Grammar" subitem="relativeURI"/><iref primary="true" item="Grammar" subitem="uri-host"/><artwork type="abnf2616"><![CDATA[
1031  absoluteURI   = <absoluteURI, defined in [RFC2396], Section 3>
1032  authority     = <authority, defined in [RFC2396], Section 3.2>
1033  fragment      = <fragment, defined in [RFC2396], Section 4.1>
1034  path-absolute = <abs_path, defined in [RFC2396], Section 3>
1035  port          = <port, defined in [RFC2396], Section 3.2.2>
1036  query         = <query, defined in [RFC2396], Section 3.4>
1037  relativeURI   = <relativeURI, defined in [RFC2396], Section 5>
1038  uri-host      = <host, defined in [RFC2396], Section 3.2.2>
1041   HTTP does not place any a priori limit on the length of
1042   a URI. Servers MUST be able to handle the URI of any resource they
1043   serve, and SHOULD be able to handle URIs of unbounded length if they
1044   provide GET-based forms that could generate such URIs. A server
1045   SHOULD return 414 (Request-URI Too Long) status if a URI is longer
1046   than the server can handle (see Section 9.4.15 of <xref target="Part2"/>).
1049  <list>
1050    <t>
1051      Note: Servers ought to be cautious about depending on URI lengths
1052      above 255 bytes, because some older client or proxy
1053      implementations might not properly support these lengths.
1054    </t>
1055  </list>
1059<section title="http URL" anchor="http.url">
1061   The "http" scheme is used to locate network resources via the HTTP
1062   protocol. This section defines the scheme-specific syntax and
1063   semantics for http URLs.
1065<figure><iref primary="true" item="Grammar" subitem="http-URL"/><artwork type="abnf2616"><![CDATA[
1066  http-URL = "http:" "//" uri-host [ ":" port ]
1067             [ path-absolute [ "?" query ]]
1070   If the port is empty or not given, port 80 is assumed. The semantics
1071   are that the identified resource is located at the server listening
1072   for TCP connections on that port of that host, and the Request-URI
1073   for the resource is path-absolute (<xref target="request-uri"/>). The use of IP addresses
1074   in URLs SHOULD be avoided whenever possible (see <xref target="RFC1900"/>). If
1075   the path-absolute is not present in the URL, it MUST be given as "/" when
1076   used as a Request-URI for a resource (<xref target="request-uri"/>). If a proxy
1077   receives a host name which is not a fully qualified domain name, it
1078   MAY add its domain to the host name it received. If a proxy receives
1079   a fully qualified domain name, the proxy MUST NOT change the host
1080   name.
1084<section title="URI Comparison" anchor="uri.comparison">
1086   When comparing two URIs to decide if they match or not, a client
1087   SHOULD use a case-sensitive octet-by-octet comparison of the entire
1088   URIs, with these exceptions:
1089  <list style="symbols">
1090    <t>A port that is empty or not given is equivalent to the default
1091        port for that URI-reference;</t>
1092    <t>Comparisons of host names MUST be case-insensitive;</t>
1093    <t>Comparisons of scheme names MUST be case-insensitive;</t>
1094    <t>An empty path-absolute is equivalent to an path-absolute of "/".</t>
1095  </list>
1098   Characters other than those in the "reserved" set (see
1099   <xref target="RFC2396"/>) are equivalent to their ""%" HEX HEX" encoding.
1102   For example, the following three URIs are equivalent:
1104<figure><artwork type="example"><![CDATA[
1112<section title="Date/Time Formats" anchor="date.time.formats">
1113<section title="Full Date" anchor="">
1115   HTTP applications have historically allowed three different formats
1116   for the representation of date/time stamps:
1118<figure><artwork type="example"><![CDATA[
1119   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
1120   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1121   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1124   The first format is preferred as an Internet standard and represents
1125   a fixed-length subset of that defined by <xref target="RFC1123"/> (an update to
1126   <xref target="RFC822"/>). The other formats are described here only for
1127   compatibility with obsolete implementations.
1128   HTTP/1.1 clients and servers that parse the date value MUST accept
1129   all three formats (for compatibility with HTTP/1.0), though they MUST
1130   only generate the RFC 1123 format for representing HTTP-date values
1131   in header fields. See <xref target="tolerant.applications"/> for further information.
1134      Note: Recipients of date values are encouraged to be robust in
1135      accepting date values that may have been sent by non-HTTP
1136      applications, as is sometimes the case when retrieving or posting
1137      messages via proxies/gateways to SMTP or NNTP.
1140   All HTTP date/time stamps MUST be represented in Greenwich Mean Time
1141   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1142   equal to UTC (Coordinated Universal Time). This is indicated in the
1143   first two formats by the inclusion of "GMT" as the three-letter
1144   abbreviation for time zone, and MUST be assumed when reading the
1145   asctime format. HTTP-date is case sensitive and MUST NOT include
1146   additional LWS beyond that specifically included as SP in the
1147   grammar.
1149<figure><iref primary="true" item="Grammar" subitem="HTTP-date"/><iref primary="true" item="Grammar" subitem="rfc1123-date"/><iref primary="true" item="Grammar" subitem="rfc850-date"/><iref primary="true" item="Grammar" subitem="asctime-date"/><iref primary="true" item="Grammar" subitem="date1"/><iref primary="true" item="Grammar" subitem="date2"/><iref primary="true" item="Grammar" subitem="date3"/><iref primary="true" item="Grammar" subitem="time"/><iref primary="true" item="Grammar" subitem="wkday"/><iref primary="true" item="Grammar" subitem="weekday"/><iref primary="true" item="Grammar" subitem="month"/><artwork type="abnf2616"><![CDATA[
1150  HTTP-date    = rfc1123-date | rfc850-date | asctime-date
1151  rfc1123-date = wkday "," SP date1 SP time SP "GMT"
1152  rfc850-date  = weekday "," SP date2 SP time SP "GMT"
1153  asctime-date = wkday SP date3 SP time SP 4DIGIT
1154  date1        = 2DIGIT SP month SP 4DIGIT
1155                 ; day month year (e.g., 02 Jun 1982)
1156  date2        = 2DIGIT "-" month "-" 2DIGIT
1157                 ; day-month-year (e.g., 02-Jun-82)
1158  date3        = month SP ( 2DIGIT | ( SP 1DIGIT ))
1159                 ; month day (e.g., Jun  2)
1160  time         = 2DIGIT ":" 2DIGIT ":" 2DIGIT
1161                 ; 00:00:00 - 23:59:59
1162  wkday        = "Mon" | "Tue" | "Wed"
1163               | "Thu" | "Fri" | "Sat" | "Sun"
1164  weekday      = "Monday" | "Tuesday" | "Wednesday"
1165               | "Thursday" | "Friday" | "Saturday" | "Sunday"
1166  month        = "Jan" | "Feb" | "Mar" | "Apr"
1167               | "May" | "Jun" | "Jul" | "Aug"
1168               | "Sep" | "Oct" | "Nov" | "Dec"
1171      Note: HTTP requirements for the date/time stamp format apply only
1172      to their usage within the protocol stream. Clients and servers are
1173      not required to use these formats for user presentation, request
1174      logging, etc.
1179<section title="Transfer Codings" anchor="transfer.codings">
1181   Transfer-coding values are used to indicate an encoding
1182   transformation that has been, can be, or may need to be applied to an
1183   entity-body in order to ensure "safe transport" through the network.
1184   This differs from a content coding in that the transfer-coding is a
1185   property of the message, not of the original entity.
1187<figure><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/><artwork type="abnf2616"><![CDATA[
1188  transfer-coding         = "chunked" | transfer-extension
1189  transfer-extension      = token *( ";" parameter )
1192   Parameters are in  the form of attribute/value pairs.
1194<figure><iref primary="true" item="Grammar" subitem="parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/><artwork type="abnf2616"><![CDATA[
1195  parameter               = attribute "=" value
1196  attribute               = token
1197  value                   = token | quoted-string
1200   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1201   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1202   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1205   Whenever a transfer-coding is applied to a message-body, the set of
1206   transfer-codings MUST include "chunked", unless the message is
1207   terminated by closing the connection. When the "chunked" transfer-coding
1208   is used, it MUST be the last transfer-coding applied to the
1209   message-body. The "chunked" transfer-coding MUST NOT be applied more
1210   than once to a message-body. These rules allow the recipient to
1211   determine the transfer-length of the message (<xref target="message.length"/>).
1214   Transfer-codings are analogous to the Content-Transfer-Encoding
1215   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
1216   binary data over a 7-bit transport service. However, safe transport
1217   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1218   the only unsafe characteristic of message-bodies is the difficulty in
1219   determining the exact body length (<xref target="message.length"/>), or the desire to
1220   encrypt data over a shared transport.
1223   The Internet Assigned Numbers Authority (IANA) acts as a registry for
1224   transfer-coding value tokens. Initially, the registry contains the
1225   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1226   "gzip", "compress", and "deflate" (Section 3.2 of <xref target="Part3"/>).
1229   New transfer-coding value tokens SHOULD be registered in the same way
1230   as new content-coding value tokens (Section 3.2 of <xref target="Part3"/>).
1233   A server which receives an entity-body with a transfer-coding it does
1234   not understand SHOULD return 501 (Not Implemented), and close the
1235   connection. A server MUST NOT send transfer-codings to an HTTP/1.0
1236   client.
1239<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1241   The chunked encoding modifies the body of a message in order to
1242   transfer it as a series of chunks, each with its own size indicator,
1243   followed by an OPTIONAL trailer containing entity-header fields. This
1244   allows dynamically produced content to be transferred along with the
1245   information necessary for the recipient to verify that it has
1246   received the full message.
1248<figure><iref primary="true" item="Grammar" subitem="Chunked-Body"/><iref primary="true" item="Grammar" subitem="chunk"/><iref primary="true" item="Grammar" subitem="chunk-size"/><iref primary="true" item="Grammar" subitem="last-chunk"/><iref primary="true" item="Grammar" subitem="chunk-extension"/><iref primary="true" item="Grammar" subitem="chunk-ext-name"/><iref primary="true" item="Grammar" subitem="chunk-ext-val"/><iref primary="true" item="Grammar" subitem="chunk-data"/><iref primary="true" item="Grammar" subitem="trailer-part"/><artwork type="abnf2616"><![CDATA[
1249  Chunked-Body   = *chunk
1250                   last-chunk
1251                   trailer-part
1252                   CRLF
1254  chunk          = chunk-size [ chunk-extension ] CRLF
1255                   chunk-data CRLF
1256  chunk-size     = 1*HEX
1257  last-chunk     = 1*("0") [ chunk-extension ] CRLF
1259  chunk-extension= *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
1260  chunk-ext-name = token
1261  chunk-ext-val  = token | quoted-string
1262  chunk-data     = 1*OCTET ; a sequence of chunk-size octets
1263  trailer-part   = *(entity-header CRLF)
1266   The chunk-size field is a string of hex digits indicating the size of
1267   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1268   zero, followed by the trailer, which is terminated by an empty line.
1271   The trailer allows the sender to include additional HTTP header
1272   fields at the end of the message. The Trailer header field can be
1273   used to indicate which header fields are included in a trailer (see
1274   <xref target="header.trailer"/>).
1277   A server using chunked transfer-coding in a response MUST NOT use the
1278   trailer for any header fields unless at least one of the following is
1279   true:
1280  <list style="numbers">
1281    <t>the request included a TE header field that indicates "trailers" is
1282     acceptable in the transfer-coding of the  response, as described in
1283     <xref target="header.te"/>; or,</t>
1285    <t>the server is the origin server for the response, the trailer
1286     fields consist entirely of optional metadata, and the recipient
1287     could use the message (in a manner acceptable to the origin server)
1288     without receiving this metadata.  In other words, the origin server
1289     is willing to accept the possibility that the trailer fields might
1290     be silently discarded along the path to the client.</t>
1291  </list>
1294   This requirement prevents an interoperability failure when the
1295   message is being received by an HTTP/1.1 (or later) proxy and
1296   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1297   compliance with the protocol would have necessitated a possibly
1298   infinite buffer on the proxy.
1301   A process for decoding the "chunked" transfer-coding
1302   can be represented in pseudo-code as:
1304<figure><artwork type="code"><![CDATA[
1305    length := 0
1306    read chunk-size, chunk-extension (if any) and CRLF
1307    while (chunk-size > 0) {
1308       read chunk-data and CRLF
1309       append chunk-data to entity-body
1310       length := length + chunk-size
1311       read chunk-size and CRLF
1312    }
1313    read entity-header
1314    while (entity-header not empty) {
1315       append entity-header to existing header fields
1316       read entity-header
1317    }
1318    Content-Length := length
1319    Remove "chunked" from Transfer-Encoding
1322   All HTTP/1.1 applications MUST be able to receive and decode the
1323   "chunked" transfer-coding, and MUST ignore chunk-extension extensions
1324   they do not understand.
1329<section title="Product Tokens" anchor="product.tokens">
1331   Product tokens are used to allow communicating applications to
1332   identify themselves by software name and version. Most fields using
1333   product tokens also allow sub-products which form a significant part
1334   of the application to be listed, separated by white space. By
1335   convention, the products are listed in order of their significance
1336   for identifying the application.
1338<figure><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/><artwork type="abnf2616"><![CDATA[
1339  product         = token ["/" product-version]
1340  product-version = token
1343   Examples:
1345<figure><artwork type="example"><![CDATA[
1346    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1347    Server: Apache/0.8.4
1350   Product tokens SHOULD be short and to the point. They MUST NOT be
1351   used for advertising or other non-essential information. Although any
1352   token character MAY appear in a product-version, this token SHOULD
1353   only be used for a version identifier (i.e., successive versions of
1354   the same product SHOULD only differ in the product-version portion of
1355   the product value).
1361<section title="HTTP Message" anchor="http.message">
1363<section title="Message Types" anchor="message.types">
1365   HTTP messages consist of requests from client to server and responses
1366   from server to client.
1368<figure><iref primary="true" item="Grammar" subitem="HTTP-message"/><artwork type="abnf2616"><![CDATA[
1369  HTTP-message   = Request | Response     ; HTTP/1.1 messages
1372   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1373   message format of <xref target="RFC2822"/> for transferring entities (the payload
1374   of the message). Both types of message consist of a start-line, zero
1375   or more header fields (also known as "headers"), an empty line (i.e.,
1376   a line with nothing preceding the CRLF) indicating the end of the
1377   header fields, and possibly a message-body.
1379<figure><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/><artwork type="abnf2616"><![CDATA[
1380  generic-message = start-line
1381                    *(message-header CRLF)
1382                    CRLF
1383                    [ message-body ]
1384  start-line      = Request-Line | Status-Line
1387   In the interest of robustness, servers SHOULD ignore any empty
1388   line(s) received where a Request-Line is expected. In other words, if
1389   the server is reading the protocol stream at the beginning of a
1390   message and receives a CRLF first, it should ignore the CRLF.
1393   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1394   after a POST request. To restate what is explicitly forbidden by the
1395   BNF, an HTTP/1.1 client MUST NOT preface or follow a request with an
1396   extra CRLF.
1400<section title="Message Headers" anchor="message.headers">
1402   HTTP header fields, which include general-header (<xref target="general.header.fields"/>),
1403   request-header (Section 4 of <xref target="Part2"/>), response-header (Section 6 of <xref target="Part2"/>), and
1404   entity-header (Section 4.1 of <xref target="Part3"/>) fields, follow the same generic format as
1405   that given in Section 2.1 of <xref target="RFC2822"/>. Each header field consists
1406   of a name followed by a colon (":") and the field value. Field names
1407   are case-insensitive. The field value MAY be preceded by any amount
1408   of LWS, though a single SP is preferred. Header fields can be
1409   extended over multiple lines by preceding each extra line with at
1410   least one SP or HTAB. Applications ought to follow "common form", where
1411   one is known or indicated, when generating HTTP constructs, since
1412   there might exist some implementations that fail to accept anything
1413   beyond the common forms.
1415<figure><iref primary="true" item="Grammar" subitem="message-header"/><iref primary="true" item="Grammar" subitem="field-name"/><iref primary="true" item="Grammar" subitem="field-value"/><iref primary="true" item="Grammar" subitem="field-content"/><artwork type="abnf2616"><![CDATA[
1416  message-header = field-name ":" [ field-value ]
1417  field-name     = token
1418  field-value    = *( field-content | LWS )
1419  field-content  = <field content>
1420                   ; the OCTETs making up the field-value
1421                   ; and consisting of either *TEXT or combinations
1422                   ; of token, separators, and quoted-string
1425   The field-content does not include any leading or trailing LWS:
1426   linear white space occurring before the first non-whitespace
1427   character of the field-value or after the last non-whitespace
1428   character of the field-value. Such leading or trailing LWS MAY be
1429   removed without changing the semantics of the field value. Any LWS
1430   that occurs between field-content MAY be replaced with a single SP
1431   before interpreting the field value or forwarding the message
1432   downstream.
1435   The order in which header fields with differing field names are
1436   received is not significant. However, it is "good practice" to send
1437   general-header fields first, followed by request-header or response-header
1438   fields, and ending with the entity-header fields.
1441   Multiple message-header fields with the same field-name MAY be
1442   present in a message if and only if the entire field-value for that
1443   header field is defined as a comma-separated list [i.e., #(values)].
1444   It MUST be possible to combine the multiple header fields into one
1445   "field-name: field-value" pair, without changing the semantics of the
1446   message, by appending each subsequent field-value to the first, each
1447   separated by a comma. The order in which header fields with the same
1448   field-name are received is therefore significant to the
1449   interpretation of the combined field value, and thus a proxy MUST NOT
1450   change the order of these field values when a message is forwarded.
1454<section title="Message Body" anchor="message.body">
1456   The message-body (if any) of an HTTP message is used to carry the
1457   entity-body associated with the request or response. The message-body
1458   differs from the entity-body only when a transfer-coding has been
1459   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1461<figure><iref primary="true" item="Grammar" subitem="message-body"/><artwork type="abnf2616"><![CDATA[
1462  message-body = entity-body
1463               | <entity-body encoded as per Transfer-Encoding>
1466   Transfer-Encoding MUST be used to indicate any transfer-codings
1467   applied by an application to ensure safe and proper transfer of the
1468   message. Transfer-Encoding is a property of the message, not of the
1469   entity, and thus MAY be added or removed by any application along the
1470   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1471   when certain transfer-codings may be used.)
1474   The rules for when a message-body is allowed in a message differ for
1475   requests and responses.
1478   The presence of a message-body in a request is signaled by the
1479   inclusion of a Content-Length or Transfer-Encoding header field in
1480   the request's message-headers. A message-body MUST NOT be included in
1481   a request if the specification of the request method (Section 3 of <xref target="Part2"/>)
1482   explicitly disallows an entity-body in requests.
1483   When a request message contains both a message-body of non-zero
1484   length and a method that does not define any semantics for that
1485   request message-body, then an origin server SHOULD either ignore
1486   the message-body or respond with an appropriate error message
1487   (e.g., 413).  A proxy or gateway, when presented the same request,
1488   SHOULD either forward the request inbound with the message-body or
1489   ignore the message-body when determining a response.
1492   For response messages, whether or not a message-body is included with
1493   a message is dependent on both the request method and the response
1494   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1495   MUST NOT include a message-body, even though the presence of entity-header
1496   fields might lead one to believe they do. All 1xx
1497   (informational), 204 (No Content), and 304 (Not Modified) responses
1498   MUST NOT include a message-body. All other responses do include a
1499   message-body, although it MAY be of zero length.
1503<section title="Message Length" anchor="message.length">
1505   The transfer-length of a message is the length of the message-body as
1506   it appears in the message; that is, after any transfer-codings have
1507   been applied. When a message-body is included with a message, the
1508   transfer-length of that body is determined by one of the following
1509   (in order of precedence):
1512  <list style="numbers">
1513    <t>
1514     Any response message which "MUST NOT" include a message-body (such
1515     as the 1xx, 204, and 304 responses and any response to a HEAD
1516     request) is always terminated by the first empty line after the
1517     header fields, regardless of the entity-header fields present in
1518     the message.
1519    </t>
1520    <t>
1521     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1522     is present, then the transfer-length is
1523     defined by use of the "chunked" transfer-coding (<xref target="transfer.codings"/>),
1524     unless the message is terminated by closing the connection.
1525    </t>
1526    <t>
1527     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1528     decimal value in OCTETs represents both the entity-length and the
1529     transfer-length. The Content-Length header field MUST NOT be sent
1530     if these two lengths are different (i.e., if a Transfer-Encoding
1531     header field is present). If a message is received with both a
1532     Transfer-Encoding header field and a Content-Length header field,
1533     the latter MUST be ignored.
1534    </t>
1535    <t>
1536     If the message uses the media type "multipart/byteranges", and the
1537     transfer-length is not otherwise specified, then this self-delimiting
1538     media type defines the transfer-length. This media type
1539     MUST NOT be used unless the sender knows that the recipient can parse
1540     it; the presence in a request of a Range header with multiple byte-range
1541     specifiers from a 1.1 client implies that the client can parse
1542     multipart/byteranges responses.
1543    <list style="empty"><t>
1544       A range header might be forwarded by a 1.0 proxy that does not
1545       understand multipart/byteranges; in this case the server MUST
1546       delimit the message using methods defined in items 1, 3 or 5 of
1547       this section.
1548    </t></list>
1549    </t>
1550    <t>
1551     By the server closing the connection. (Closing the connection
1552     cannot be used to indicate the end of a request body, since that
1553     would leave no possibility for the server to send back a response.)
1554    </t>
1555  </list>
1558   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1559   containing a message-body MUST include a valid Content-Length header
1560   field unless the server is known to be HTTP/1.1 compliant. If a
1561   request contains a message-body and a Content-Length is not given,
1562   the server SHOULD respond with 400 (Bad Request) if it cannot
1563   determine the length of the message, or with 411 (Length Required) if
1564   it wishes to insist on receiving a valid Content-Length.
1567   All HTTP/1.1 applications that receive entities MUST accept the
1568   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1569   to be used for messages when the message length cannot be determined
1570   in advance.
1573   Messages MUST NOT include both a Content-Length header field and a
1574   transfer-coding. If the message does include a
1575   transfer-coding, the Content-Length MUST be ignored.
1578   When a Content-Length is given in a message where a message-body is
1579   allowed, its field value MUST exactly match the number of OCTETs in
1580   the message-body. HTTP/1.1 user agents MUST notify the user when an
1581   invalid length is received and detected.
1585<section title="General Header Fields" anchor="general.header.fields">
1587   There are a few header fields which have general applicability for
1588   both request and response messages, but which do not apply to the
1589   entity being transferred. These header fields apply only to the
1590   message being transmitted.
1592<figure><iref primary="true" item="Grammar" subitem="general-header"/><artwork type="abnf2616"><![CDATA[
1593  general-header = Cache-Control            ; [Part6], Section 16.2
1594                 | Connection               ; Section 8.1
1595                 | Date                     ; Section 8.3
1596                 | Pragma                   ; [Part6], Section 16.4
1597                 | Trailer                  ; Section 8.6
1598                 | Transfer-Encoding        ; Section 8.7
1599                 | Upgrade                  ; Section 8.8
1600                 | Via                      ; Section 8.9
1601                 | Warning                  ; [Part6], Section 16.6
1604   General-header field names can be extended reliably only in
1605   combination with a change in the protocol version. However, new or
1606   experimental header fields may be given the semantics of general
1607   header fields if all parties in the communication recognize them to
1608   be general-header fields. Unrecognized header fields are treated as
1609   entity-header fields.
1614<section title="Request" anchor="request">
1616   A request message from a client to a server includes, within the
1617   first line of that message, the method to be applied to the resource,
1618   the identifier of the resource, and the protocol version in use.
1620<!--                 Host                      ; should be moved here eventually -->
1621<figure><iref primary="true" item="Grammar" subitem="Request"/><artwork type="abnf2616"><![CDATA[
1622  Request       = Request-Line              ; Section 5.1
1623                  *(( general-header        ; Section 4.5
1624                   | request-header         ; [Part2], Section 4
1625                   | entity-header ) CRLF)  ; [Part3], Section 4.1
1626                  CRLF
1627                  [ message-body ]          ; Section 4.3
1630<section title="Request-Line" anchor="request-line">
1632   The Request-Line begins with a method token, followed by the
1633   Request-URI and the protocol version, and ending with CRLF. The
1634   elements are separated by SP characters. No CR or LF is allowed
1635   except in the final CRLF sequence.
1637<figure><iref primary="true" item="Grammar" subitem="Request-Line"/><artwork type="abnf2616"><![CDATA[
1638  Request-Line   = Method SP Request-URI SP HTTP-Version CRLF
1641<section title="Method" anchor="method">
1643   The Method  token indicates the method to be performed on the
1644   resource identified by the Request-URI. The method is case-sensitive.
1646<figure><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/><artwork type="abnf2616"><![CDATA[
1647  Method         = token
1651<section title="Request-URI" anchor="request-uri">
1653   The Request-URI is a Uniform Resource Identifier (<xref target="uri"/>) and
1654   identifies the resource upon which to apply the request.
1656<figure><iref primary="true" item="Grammar" subitem="Request-URI"/><artwork type="abnf2616"><![CDATA[
1657  Request-URI    = "*"
1658                 | absoluteURI
1659                 | ( path-absolute [ "?" query ] )
1660                 | authority
1663   The four options for Request-URI are dependent on the nature of the
1664   request. The asterisk "*" means that the request does not apply to a
1665   particular resource, but to the server itself, and is only allowed
1666   when the method used does not necessarily apply to a resource. One
1667   example would be
1669<figure><artwork type="example"><![CDATA[
1670    OPTIONS * HTTP/1.1
1673   The absoluteURI form is REQUIRED when the request is being made to a
1674   proxy. The proxy is requested to forward the request or service it
1675   from a valid cache, and return the response. Note that the proxy MAY
1676   forward the request on to another proxy or directly to the server
1677   specified by the absoluteURI. In order to avoid request loops, a
1678   proxy MUST be able to recognize all of its server names, including
1679   any aliases, local variations, and the numeric IP address. An example
1680   Request-Line would be:
1682<figure><artwork type="example"><![CDATA[
1683    GET HTTP/1.1
1686   To allow for transition to absoluteURIs in all requests in future
1687   versions of HTTP, all HTTP/1.1 servers MUST accept the absoluteURI
1688   form in requests, even though HTTP/1.1 clients will only generate
1689   them in requests to proxies.
1692   The authority form is only used by the CONNECT method (Section 8.9 of <xref target="Part2"/>).
1695   The most common form of Request-URI is that used to identify a
1696   resource on an origin server or gateway. In this case the absolute
1697   path of the URI MUST be transmitted (see <xref target="general.syntax"/>, path-absolute) as
1698   the Request-URI, and the network location of the URI (authority) MUST
1699   be transmitted in a Host header field. For example, a client wishing
1700   to retrieve the resource above directly from the origin server would
1701   create a TCP connection to port 80 of the host "" and send
1702   the lines:
1704<figure><artwork type="example"><![CDATA[
1705    GET /pub/WWW/TheProject.html HTTP/1.1
1706    Host:
1709   followed by the remainder of the Request. Note that the absolute path
1710   cannot be empty; if none is present in the original URI, it MUST be
1711   given as "/" (the server root).
1714   The Request-URI is transmitted in the format specified in
1715   <xref target="general.syntax"/>. If the Request-URI is encoded using the "% HEX HEX" encoding
1716   <xref target="RFC2396"/>, the origin server MUST decode the Request-URI in order to
1717   properly interpret the request. Servers SHOULD respond to invalid
1718   Request-URIs with an appropriate status code.
1721   A transparent proxy MUST NOT rewrite the "path-absolute" part of the
1722   received Request-URI when forwarding it to the next inbound server,
1723   except as noted above to replace a null path-absolute with "/".
1726  <list><t>
1727      Note: The "no rewrite" rule prevents the proxy from changing the
1728      meaning of the request when the origin server is improperly using
1729      a non-reserved URI character for a reserved purpose.  Implementors
1730      should be aware that some pre-HTTP/1.1 proxies have been known to
1731      rewrite the Request-URI.
1732  </t></list>
1737<section title="The Resource Identified by a Request" anchor="">
1739   The exact resource identified by an Internet request is determined by
1740   examining both the Request-URI and the Host header field.
1743   An origin server that does not allow resources to differ by the
1744   requested host MAY ignore the Host header field value when
1745   determining the resource identified by an HTTP/1.1 request. (But see
1746   <xref target=""/>
1747   for other requirements on Host support in HTTP/1.1.)
1750   An origin server that does differentiate resources based on the host
1751   requested (sometimes referred to as virtual hosts or vanity host
1752   names) MUST use the following rules for determining the requested
1753   resource on an HTTP/1.1 request:
1754  <list style="numbers">
1755    <t>If Request-URI is an absoluteURI, the host is part of the
1756     Request-URI. Any Host header field value in the request MUST be
1757     ignored.</t>
1758    <t>If the Request-URI is not an absoluteURI, and the request includes
1759     a Host header field, the host is determined by the Host header
1760     field value.</t>
1761    <t>If the host as determined by rule 1 or 2 is not a valid host on
1762     the server, the response MUST be a 400 (Bad Request) error message.</t>
1763  </list>
1766   Recipients of an HTTP/1.0 request that lacks a Host header field MAY
1767   attempt to use heuristics (e.g., examination of the URI path for
1768   something unique to a particular host) in order to determine what
1769   exact resource is being requested.
1776<section title="Response" anchor="response">
1778   After receiving and interpreting a request message, a server responds
1779   with an HTTP response message.
1781<figure><iref primary="true" item="Grammar" subitem="Response"/><artwork type="abnf2616"><![CDATA[
1782  Response      = Status-Line               ; Section 6.1
1783                  *(( general-header        ; Section 4.5
1784                   | response-header        ; [Part2], Section 6
1785                   | entity-header ) CRLF)  ; [Part3], Section 4.1
1786                  CRLF
1787                  [ message-body ]          ; Section 4.3
1790<section title="Status-Line" anchor="status-line">
1792   The first line of a Response message is the Status-Line, consisting
1793   of the protocol version followed by a numeric status code and its
1794   associated textual phrase, with each element separated by SP
1795   characters. No CR or LF is allowed except in the final CRLF sequence.
1797<figure><iref primary="true" item="Grammar" subitem="Status-Line"/><artwork type="abnf2616"><![CDATA[
1798  Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
1801<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1803   The Status-Code element is a 3-digit integer result code of the
1804   attempt to understand and satisfy the request. These codes are fully
1805   defined in Section 9 of <xref target="Part2"/>.  The Reason Phrase exists for the sole
1806   purpose of providing a textual description associated with the numeric
1807   status code, out of deference to earlier Internet application protocols
1808   that were more frequently used with interactive text clients.
1809   A client SHOULD ignore the content of the Reason Phrase.
1812   The first digit of the Status-Code defines the class of response. The
1813   last two digits do not have any categorization role. There are 5
1814   values for the first digit:
1815  <list style="symbols">
1816    <t>
1817      1xx: Informational - Request received, continuing process
1818    </t>
1819    <t>
1820      2xx: Success - The action was successfully received,
1821        understood, and accepted
1822    </t>
1823    <t>
1824      3xx: Redirection - Further action must be taken in order to
1825        complete the request
1826    </t>
1827    <t>
1828      4xx: Client Error - The request contains bad syntax or cannot
1829        be fulfilled
1830    </t>
1831    <t>
1832      5xx: Server Error - The server failed to fulfill an apparently
1833        valid request
1834    </t>
1835  </list>
1837<figure><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="extension-code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/><artwork type="abnf2616"><![CDATA[
1838  Status-Code    = 3DIGIT
1839  Reason-Phrase  = *<TEXT, excluding CR, LF>
1847<section title="Connections" anchor="connections">
1849<section title="Persistent Connections" anchor="persistent.connections">
1851<section title="Purpose" anchor="persistent.purpose">
1853   Prior to persistent connections, a separate TCP connection was
1854   established to fetch each URL, increasing the load on HTTP servers
1855   and causing congestion on the Internet. The use of inline images and
1856   other associated data often require a client to make multiple
1857   requests of the same server in a short amount of time. Analysis of
1858   these performance problems and results from a prototype
1859   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1860   measurements of actual HTTP/1.1 (RFC 2068) implementations show good
1861   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1862   T/TCP <xref target="Tou1998"/>.
1865   Persistent HTTP connections have a number of advantages:
1866  <list style="symbols">
1867      <t>
1868        By opening and closing fewer TCP connections, CPU time is saved
1869        in routers and hosts (clients, servers, proxies, gateways,
1870        tunnels, or caches), and memory used for TCP protocol control
1871        blocks can be saved in hosts.
1872      </t>
1873      <t>
1874        HTTP requests and responses can be pipelined on a connection.
1875        Pipelining allows a client to make multiple requests without
1876        waiting for each response, allowing a single TCP connection to
1877        be used much more efficiently, with much lower elapsed time.
1878      </t>
1879      <t>
1880        Network congestion is reduced by reducing the number of packets
1881        caused by TCP opens, and by allowing TCP sufficient time to
1882        determine the congestion state of the network.
1883      </t>
1884      <t>
1885        Latency on subsequent requests is reduced since there is no time
1886        spent in TCP's connection opening handshake.
1887      </t>
1888      <t>
1889        HTTP can evolve more gracefully, since errors can be reported
1890        without the penalty of closing the TCP connection. Clients using
1891        future versions of HTTP might optimistically try a new feature,
1892        but if communicating with an older server, retry with old
1893        semantics after an error is reported.
1894      </t>
1895    </list>
1898   HTTP implementations SHOULD implement persistent connections.
1902<section title="Overall Operation" anchor="persistent.overall">
1904   A significant difference between HTTP/1.1 and earlier versions of
1905   HTTP is that persistent connections are the default behavior of any
1906   HTTP connection. That is, unless otherwise indicated, the client
1907   SHOULD assume that the server will maintain a persistent connection,
1908   even after error responses from the server.
1911   Persistent connections provide a mechanism by which a client and a
1912   server can signal the close of a TCP connection. This signaling takes
1913   place using the Connection header field (<xref target="header.connection"/>). Once a close
1914   has been signaled, the client MUST NOT send any more requests on that
1915   connection.
1918<section title="Negotiation" anchor="persistent.negotiation">
1920   An HTTP/1.1 server MAY assume that a HTTP/1.1 client intends to
1921   maintain a persistent connection unless a Connection header including
1922   the connection-token "close" was sent in the request. If the server
1923   chooses to close the connection immediately after sending the
1924   response, it SHOULD send a Connection header including the
1925   connection-token close.
1928   An HTTP/1.1 client MAY expect a connection to remain open, but would
1929   decide to keep it open based on whether the response from a server
1930   contains a Connection header with the connection-token close. In case
1931   the client does not want to maintain a connection for more than that
1932   request, it SHOULD send a Connection header including the
1933   connection-token close.
1936   If either the client or the server sends the close token in the
1937   Connection header, that request becomes the last one for the
1938   connection.
1941   Clients and servers SHOULD NOT  assume that a persistent connection is
1942   maintained for HTTP versions less than 1.1 unless it is explicitly
1943   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1944   compatibility with HTTP/1.0 clients.
1947   In order to remain persistent, all messages on the connection MUST
1948   have a self-defined message length (i.e., one not defined by closure
1949   of the connection), as described in <xref target="message.length"/>.
1953<section title="Pipelining" anchor="pipelining">
1955   A client that supports persistent connections MAY "pipeline" its
1956   requests (i.e., send multiple requests without waiting for each
1957   response). A server MUST send its responses to those requests in the
1958   same order that the requests were received.
1961   Clients which assume persistent connections and pipeline immediately
1962   after connection establishment SHOULD be prepared to retry their
1963   connection if the first pipelined attempt fails. If a client does
1964   such a retry, it MUST NOT pipeline before it knows the connection is
1965   persistent. Clients MUST also be prepared to resend their requests if
1966   the server closes the connection before sending all of the
1967   corresponding responses.
1970   Clients SHOULD NOT  pipeline requests using non-idempotent methods or
1971   non-idempotent sequences of methods (see Section 8.1.2 of <xref target="Part2"/>). Otherwise, a
1972   premature termination of the transport connection could lead to
1973   indeterminate results. A client wishing to send a non-idempotent
1974   request SHOULD wait to send that request until it has received the
1975   response status for the previous request.
1980<section title="Proxy Servers" anchor="persistent.proxy">
1982   It is especially important that proxies correctly implement the
1983   properties of the Connection header field as specified in <xref target="header.connection"/>.
1986   The proxy server MUST signal persistent connections separately with
1987   its clients and the origin servers (or other proxy servers) that it
1988   connects to. Each persistent connection applies to only one transport
1989   link.
1992   A proxy server MUST NOT establish a HTTP/1.1 persistent connection
1993   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1994   discussion of the problems with the Keep-Alive header implemented by
1995   many HTTP/1.0 clients).
1999<section title="Practical Considerations" anchor="persistent.practical">
2001   Servers will usually have some time-out value beyond which they will
2002   no longer maintain an inactive connection. Proxy servers might make
2003   this a higher value since it is likely that the client will be making
2004   more connections through the same server. The use of persistent
2005   connections places no requirements on the length (or existence) of
2006   this time-out for either the client or the server.
2009   When a client or server wishes to time-out it SHOULD issue a graceful
2010   close on the transport connection. Clients and servers SHOULD both
2011   constantly watch for the other side of the transport close, and
2012   respond to it as appropriate. If a client or server does not detect
2013   the other side's close promptly it could cause unnecessary resource
2014   drain on the network.
2017   A client, server, or proxy MAY close the transport connection at any
2018   time. For example, a client might have started to send a new request
2019   at the same time that the server has decided to close the "idle"
2020   connection. From the server's point of view, the connection is being
2021   closed while it was idle, but from the client's point of view, a
2022   request is in progress.
2025   This means that clients, servers, and proxies MUST be able to recover
2026   from asynchronous close events. Client software SHOULD reopen the
2027   transport connection and retransmit the aborted sequence of requests
2028   without user interaction so long as the request sequence is
2029   idempotent (see Section 8.1.2 of <xref target="Part2"/>). Non-idempotent methods or sequences
2030   MUST NOT be automatically retried, although user agents MAY offer a
2031   human operator the choice of retrying the request(s). Confirmation by
2032   user-agent software with semantic understanding of the application
2033   MAY substitute for user confirmation. The automatic retry SHOULD NOT
2034   be repeated if the second sequence of requests fails.
2037   Servers SHOULD always respond to at least one request per connection,
2038   if at all possible. Servers SHOULD NOT  close a connection in the
2039   middle of transmitting a response, unless a network or client failure
2040   is suspected.
2043   Clients that use persistent connections SHOULD limit the number of
2044   simultaneous connections that they maintain to a given server. A
2045   single-user client SHOULD NOT maintain more than 2 connections with
2046   any server or proxy. A proxy SHOULD use up to 2*N connections to
2047   another server or proxy, where N is the number of simultaneously
2048   active users. These guidelines are intended to improve HTTP response
2049   times and avoid congestion.
2054<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2056<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2058   HTTP/1.1 servers SHOULD maintain persistent connections and use TCP's
2059   flow control mechanisms to resolve temporary overloads, rather than
2060   terminating connections with the expectation that clients will retry.
2061   The latter technique can exacerbate network congestion.
2065<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2067   An HTTP/1.1 (or later) client sending a message-body SHOULD monitor
2068   the network connection for an error status while it is transmitting
2069   the request. If the client sees an error status, it SHOULD
2070   immediately cease transmitting the body. If the body is being sent
2071   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2072   empty trailer MAY be used to prematurely mark the end of the message.
2073   If the body was preceded by a Content-Length header, the client MUST
2074   close the connection.
2078<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2080   The purpose of the 100 (Continue) status (see Section 9.1.1 of <xref target="Part2"/>) is to
2081   allow a client that is sending a request message with a request body
2082   to determine if the origin server is willing to accept the request
2083   (based on the request headers) before the client sends the request
2084   body. In some cases, it might either be inappropriate or highly
2085   inefficient for the client to send the body if the server will reject
2086   the message without looking at the body.
2089   Requirements for HTTP/1.1 clients:
2090  <list style="symbols">
2091    <t>
2092        If a client will wait for a 100 (Continue) response before
2093        sending the request body, it MUST send an Expect request-header
2094        field (Section 10.2 of <xref target="Part2"/>) with the "100-continue" expectation.
2095    </t>
2096    <t>
2097        A client MUST NOT send an Expect request-header field (Section 10.2 of <xref target="Part2"/>)
2098        with the "100-continue" expectation if it does not intend
2099        to send a request body.
2100    </t>
2101  </list>
2104   Because of the presence of older implementations, the protocol allows
2105   ambiguous situations in which a client may send "Expect: 100-continue"
2106   without receiving either a 417 (Expectation Failed) status
2107   or a 100 (Continue) status. Therefore, when a client sends this
2108   header field to an origin server (possibly via a proxy) from which it
2109   has never seen a 100 (Continue) status, the client SHOULD NOT  wait
2110   for an indefinite period before sending the request body.
2113   Requirements for HTTP/1.1 origin servers:
2114  <list style="symbols">
2115    <t> Upon receiving a request which includes an Expect request-header
2116        field with the "100-continue" expectation, an origin server MUST
2117        either respond with 100 (Continue) status and continue to read
2118        from the input stream, or respond with a final status code. The
2119        origin server MUST NOT wait for the request body before sending
2120        the 100 (Continue) response. If it responds with a final status
2121        code, it MAY close the transport connection or it MAY continue
2122        to read and discard the rest of the request.  It MUST NOT
2123        perform the requested method if it returns a final status code.
2124    </t>
2125    <t> An origin server SHOULD NOT  send a 100 (Continue) response if
2126        the request message does not include an Expect request-header
2127        field with the "100-continue" expectation, and MUST NOT send a
2128        100 (Continue) response if such a request comes from an HTTP/1.0
2129        (or earlier) client. There is an exception to this rule: for
2130        compatibility with <xref target="RFC2068"/>, a server MAY send a 100 (Continue)
2131        status in response to an HTTP/1.1 PUT or POST request that does
2132        not include an Expect request-header field with the "100-continue"
2133        expectation. This exception, the purpose of which is
2134        to minimize any client processing delays associated with an
2135        undeclared wait for 100 (Continue) status, applies only to
2136        HTTP/1.1 requests, and not to requests with any other HTTP-version
2137        value.
2138    </t>
2139    <t> An origin server MAY omit a 100 (Continue) response if it has
2140        already received some or all of the request body for the
2141        corresponding request.
2142    </t>
2143    <t> An origin server that sends a 100 (Continue) response MUST
2144    ultimately send a final status code, once the request body is
2145        received and processed, unless it terminates the transport
2146        connection prematurely.
2147    </t>
2148    <t> If an origin server receives a request that does not include an
2149        Expect request-header field with the "100-continue" expectation,
2150        the request includes a request body, and the server responds
2151        with a final status code before reading the entire request body
2152        from the transport connection, then the server SHOULD NOT  close
2153        the transport connection until it has read the entire request,
2154        or until the client closes the connection. Otherwise, the client
2155        might not reliably receive the response message. However, this
2156        requirement is not be construed as preventing a server from
2157        defending itself against denial-of-service attacks, or from
2158        badly broken client implementations.
2159      </t>
2160    </list>
2163   Requirements for HTTP/1.1 proxies:
2164  <list style="symbols">
2165    <t> If a proxy receives a request that includes an Expect request-header
2166        field with the "100-continue" expectation, and the proxy
2167        either knows that the next-hop server complies with HTTP/1.1 or
2168        higher, or does not know the HTTP version of the next-hop
2169        server, it MUST forward the request, including the Expect header
2170        field.
2171    </t>
2172    <t> If the proxy knows that the version of the next-hop server is
2173        HTTP/1.0 or lower, it MUST NOT forward the request, and it MUST
2174        respond with a 417 (Expectation Failed) status.
2175    </t>
2176    <t> Proxies SHOULD maintain a cache recording the HTTP version
2177        numbers received from recently-referenced next-hop servers.
2178    </t>
2179    <t> A proxy MUST NOT forward a 100 (Continue) response if the
2180        request message was received from an HTTP/1.0 (or earlier)
2181        client and did not include an Expect request-header field with
2182        the "100-continue" expectation. This requirement overrides the
2183        general rule for forwarding of 1xx responses (see Section 9.1 of <xref target="Part2"/>).
2184    </t>
2185  </list>
2189<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2191   If an HTTP/1.1 client sends a request which includes a request body,
2192   but which does not include an Expect request-header field with the
2193   "100-continue" expectation, and if the client is not directly
2194   connected to an HTTP/1.1 origin server, and if the client sees the
2195   connection close before receiving any status from the server, the
2196   client SHOULD retry the request.  If the client does retry this
2197   request, it MAY use the following "binary exponential backoff"
2198   algorithm to be assured of obtaining a reliable response:
2199  <list style="numbers">
2200    <t>
2201      Initiate a new connection to the server
2202    </t>
2203    <t>
2204      Transmit the request-headers
2205    </t>
2206    <t>
2207      Initialize a variable R to the estimated round-trip time to the
2208         server (e.g., based on the time it took to establish the
2209         connection), or to a constant value of 5 seconds if the round-trip
2210         time is not available.
2211    </t>
2212    <t>
2213       Compute T = R * (2**N), where N is the number of previous
2214         retries of this request.
2215    </t>
2216    <t>
2217       Wait either for an error response from the server, or for T
2218         seconds (whichever comes first)
2219    </t>
2220    <t>
2221       If no error response is received, after T seconds transmit the
2222         body of the request.
2223    </t>
2224    <t>
2225       If client sees that the connection is closed prematurely,
2226         repeat from step 1 until the request is accepted, an error
2227         response is received, or the user becomes impatient and
2228         terminates the retry process.
2229    </t>
2230  </list>
2233   If at any point an error status is received, the client
2234  <list style="symbols">
2235      <t>SHOULD NOT  continue and</t>
2237      <t>SHOULD close the connection if it has not completed sending the
2238        request message.</t>
2239    </list>
2246<section title="Header Field Definitions" anchor="header.fields">
2248   This section defines the syntax and semantics of HTTP/1.1 header fields
2249   related to message framing and transport protocols.
2252   For entity-header fields, both sender and recipient refer to either the
2253   client or the server, depending on who sends and who receives the entity.
2256<section title="Connection" anchor="header.connection">
2257  <iref primary="true" item="Connection header"/>
2258  <iref primary="true" item="Headers" subitem="Connection"/>
2260   The Connection general-header field allows the sender to specify
2261   options that are desired for that particular connection and MUST NOT
2262   be communicated by proxies over further connections.
2265   The Connection header has the following grammar:
2267<figure><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/><artwork type="abnf2616"><![CDATA[
2268  Connection = "Connection" ":" 1#(connection-token)
2269  connection-token  = token
2272   HTTP/1.1 proxies MUST parse the Connection header field before a
2273   message is forwarded and, for each connection-token in this field,
2274   remove any header field(s) from the message with the same name as the
2275   connection-token. Connection options are signaled by the presence of
2276   a connection-token in the Connection header field, not by any
2277   corresponding additional header field(s), since the additional header
2278   field may not be sent if there are no parameters associated with that
2279   connection option.
2282   Message headers listed in the Connection header MUST NOT include
2283   end-to-end headers, such as Cache-Control.
2286   HTTP/1.1 defines the "close" connection option for the sender to
2287   signal that the connection will be closed after completion of the
2288   response. For example,
2290<figure><artwork type="example"><![CDATA[
2291    Connection: close
2294   in either the request or the response header fields indicates that
2295   the connection SHOULD NOT  be considered `persistent' (<xref target="persistent.connections"/>)
2296   after the current request/response is complete.
2299   An HTTP/1.1 client that does not support persistent connections MUST
2300   include the "close" connection option in every request message.
2303   An HTTP/1.1 server that does not support persistent connections MUST
2304   include the "close" connection option in every response message that
2305   does not have a 1xx (informational) status code.
2308   A system receiving an HTTP/1.0 (or lower-version) message that
2309   includes a Connection header MUST, for each connection-token in this
2310   field, remove and ignore any header field(s) from the message with
2311   the same name as the connection-token. This protects against mistaken
2312   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2316<section title="Content-Length" anchor="header.content-length">
2317  <iref primary="true" item="Content-Length header"/>
2318  <iref primary="true" item="Headers" subitem="Content-Length"/>
2320   The Content-Length entity-header field indicates the size of the
2321   entity-body, in decimal number of OCTETs, sent to the recipient or,
2322   in the case of the HEAD method, the size of the entity-body that
2323   would have been sent had the request been a GET.
2325<figure><iref primary="true" item="Grammar" subitem="Content-Length"/><artwork type="abnf2616"><![CDATA[
2326  Content-Length    = "Content-Length" ":" 1*DIGIT
2329   An example is
2331<figure><artwork type="example"><![CDATA[
2332    Content-Length: 3495
2335   Applications SHOULD use this field to indicate the transfer-length of
2336   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2339   Any Content-Length greater than or equal to zero is a valid value.
2340   <xref target="message.length"/> describes how to determine the length of a message-body
2341   if a Content-Length is not given.
2344   Note that the meaning of this field is significantly different from
2345   the corresponding definition in MIME, where it is an optional field
2346   used within the "message/external-body" content-type. In HTTP, it
2347   SHOULD be sent whenever the message's length can be determined prior
2348   to being transferred, unless this is prohibited by the rules in
2349   <xref target="message.length"/>.
2353<section title="Date" anchor="">
2354  <iref primary="true" item="Date header"/>
2355  <iref primary="true" item="Headers" subitem="Date"/>
2357   The Date general-header field represents the date and time at which
2358   the message was originated, having the same semantics as orig-date in
2359   Section 3.6.1 of <xref target="RFC2822"/>. The field value is an HTTP-date, as described in <xref target=""/>;
2360   it MUST be sent in rfc1123-date format.
2362<figure><iref primary="true" item="Grammar" subitem="Date"/><artwork type="abnf2616"><![CDATA[
2363  Date  = "Date" ":" HTTP-date
2366   An example is
2368<figure><artwork type="example"><![CDATA[
2369    Date: Tue, 15 Nov 1994 08:12:31 GMT
2372   Origin servers MUST include a Date header field in all responses,
2373   except in these cases:
2374  <list style="numbers">
2375      <t>If the response status code is 100 (Continue) or 101 (Switching
2376         Protocols), the response MAY include a Date header field, at
2377         the server's option.</t>
2379      <t>If the response status code conveys a server error, e.g. 500
2380         (Internal Server Error) or 503 (Service Unavailable), and it is
2381         inconvenient or impossible to generate a valid Date.</t>
2383      <t>If the server does not have a clock that can provide a
2384         reasonable approximation of the current time, its responses
2385         MUST NOT include a Date header field. In this case, the rules
2386         in <xref target="clockless.origin.server.operation"/> MUST be followed.</t>
2387  </list>
2390   A received message that does not have a Date header field MUST be
2391   assigned one by the recipient if the message will be cached by that
2392   recipient or gatewayed via a protocol which requires a Date. An HTTP
2393   implementation without a clock MUST NOT cache responses without
2394   revalidating them on every use. An HTTP cache, especially a shared
2395   cache, SHOULD use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2396   clock with a reliable external standard.
2399   Clients SHOULD only send a Date header field in messages that include
2400   an entity-body, as in the case of the PUT and POST requests, and even
2401   then it is optional. A client without a clock MUST NOT send a Date
2402   header field in a request.
2405   The HTTP-date sent in a Date header SHOULD NOT  represent a date and
2406   time subsequent to the generation of the message. It SHOULD represent
2407   the best available approximation of the date and time of message
2408   generation, unless the implementation has no means of generating a
2409   reasonably accurate date and time. In theory, the date ought to
2410   represent the moment just before the entity is generated. In
2411   practice, the date can be generated at any time during the message
2412   origination without affecting its semantic value.
2415<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2417   Some origin server implementations might not have a clock available.
2418   An origin server without a clock MUST NOT assign Expires or Last-Modified
2419   values to a response, unless these values were associated
2420   with the resource by a system or user with a reliable clock. It MAY
2421   assign an Expires value that is known, at or before server
2422   configuration time, to be in the past (this allows "pre-expiration"
2423   of responses without storing separate Expires values for each
2424   resource).
2429<section title="Host" anchor="">
2430  <iref primary="true" item="Host header"/>
2431  <iref primary="true" item="Headers" subitem="Host"/>
2433   The Host request-header field specifies the Internet host and port
2434   number of the resource being requested, as obtained from the original
2435   URI given by the user or referring resource (generally an HTTP URL,
2436   as described in <xref target="http.url"/>). The Host field value MUST represent
2437   the naming authority of the origin server or gateway given by the
2438   original URL. This allows the origin server or gateway to
2439   differentiate between internally-ambiguous URLs, such as the root "/"
2440   URL of a server for multiple host names on a single IP address.
2442<figure><iref primary="true" item="Grammar" subitem="Host"/><artwork type="abnf2616"><![CDATA[
2443  Host = "Host" ":" uri-host [ ":" port ] ; Section 3.2.2
2446   A "host" without any trailing port information implies the default
2447   port for the service requested (e.g., "80" for an HTTP URL). For
2448   example, a request on the origin server for
2449   &lt;; would properly include:
2451<figure><artwork type="example"><![CDATA[
2452    GET /pub/WWW/ HTTP/1.1
2453    Host:
2456   A client MUST include a Host header field in all HTTP/1.1 request
2457   messages. If the requested URI does not include an Internet host
2458   name for the service being requested, then the Host header field MUST
2459   be given with an empty value. An HTTP/1.1 proxy MUST ensure that any
2460   request message it forwards does contain an appropriate Host header
2461   field that identifies the service being requested by the proxy. All
2462   Internet-based HTTP/1.1 servers MUST respond with a 400 (Bad Request)
2463   status code to any HTTP/1.1 request message which lacks a Host header
2464   field.
2467   See Sections <xref target="" format="counter"/>
2468   and <xref target="" format="counter"/>
2469   for other requirements relating to Host.
2473<section title="TE" anchor="header.te">
2474  <iref primary="true" item="TE header"/>
2475  <iref primary="true" item="Headers" subitem="TE"/>
2477   The TE request-header field indicates what extension transfer-codings
2478   it is willing to accept in the response and whether or not it is
2479   willing to accept trailer fields in a chunked transfer-coding. Its
2480   value may consist of the keyword "trailers" and/or a comma-separated
2481   list of extension transfer-coding names with optional accept
2482   parameters (as described in <xref target="transfer.codings"/>).
2484<figure><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/><artwork type="abnf2616"><![CDATA[
2485  TE        = "TE" ":" #( t-codings )
2486  t-codings = "trailers" | ( transfer-extension [ accept-params ] )
2489   The presence of the keyword "trailers" indicates that the client is
2490   willing to accept trailer fields in a chunked transfer-coding, as
2491   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2492   transfer-coding values even though it does not itself represent a
2493   transfer-coding.
2496   Examples of its use are:
2498<figure><artwork type="example"><![CDATA[
2499    TE: deflate
2500    TE:
2501    TE: trailers, deflate;q=0.5
2504   The TE header field only applies to the immediate connection.
2505   Therefore, the keyword MUST be supplied within a Connection header
2506   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2509   A server tests whether a transfer-coding is acceptable, according to
2510   a TE field, using these rules:
2511  <list style="numbers">
2512    <t>The "chunked" transfer-coding is always acceptable. If the
2513         keyword "trailers" is listed, the client indicates that it is
2514         willing to accept trailer fields in the chunked response on
2515         behalf of itself and any downstream clients. The implication is
2516         that, if given, the client is stating that either all
2517         downstream clients are willing to accept trailer fields in the
2518         forwarded response, or that it will attempt to buffer the
2519         response on behalf of downstream recipients.
2520      <vspace blankLines="1"/>
2521         Note: HTTP/1.1 does not define any means to limit the size of a
2522         chunked response such that a client can be assured of buffering
2523         the entire response.</t>
2524    <t>If the transfer-coding being tested is one of the transfer-codings
2525         listed in the TE field, then it is acceptable unless it
2526         is accompanied by a qvalue of 0. (As defined in Section 3.4 of <xref target="Part3"/>, a
2527         qvalue of 0 means "not acceptable.")</t>
2528    <t>If multiple transfer-codings are acceptable, then the
2529         acceptable transfer-coding with the highest non-zero qvalue is
2530         preferred.  The "chunked" transfer-coding always has a qvalue
2531         of 1.</t>
2532  </list>
2535   If the TE field-value is empty or if no TE field is present, the only
2536   transfer-coding  is "chunked". A message with no transfer-coding is
2537   always acceptable.
2541<section title="Trailer" anchor="header.trailer">
2542  <iref primary="true" item="Trailer header"/>
2543  <iref primary="true" item="Headers" subitem="Trailer"/>
2545   The Trailer general field value indicates that the given set of
2546   header fields is present in the trailer of a message encoded with
2547   chunked transfer-coding.
2549<figure><iref primary="true" item="Grammar" subitem="Trailer"/><artwork type="abnf2616"><![CDATA[
2550  Trailer  = "Trailer" ":" 1#field-name
2553   An HTTP/1.1 message SHOULD include a Trailer header field in a
2554   message using chunked transfer-coding with a non-empty trailer. Doing
2555   so allows the recipient to know which header fields to expect in the
2556   trailer.
2559   If no Trailer header field is present, the trailer SHOULD NOT  include
2560   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2561   trailer fields in a "chunked" transfer-coding.
2564   Message header fields listed in the Trailer header field MUST NOT
2565   include the following header fields:
2566  <list style="symbols">
2567    <t>Transfer-Encoding</t>
2568    <t>Content-Length</t>
2569    <t>Trailer</t>
2570  </list>
2574<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2575  <iref primary="true" item="Transfer-Encoding header"/>
2576  <iref primary="true" item="Headers" subitem="Transfer-Encoding"/>
2578   The Transfer-Encoding general-header field indicates what (if any)
2579   type of transformation has been applied to the message body in order
2580   to safely transfer it between the sender and the recipient. This
2581   differs from the content-coding in that the transfer-coding is a
2582   property of the message, not of the entity.
2584<figure><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><artwork type="abnf2616"><![CDATA[
2585  Transfer-Encoding       = "Transfer-Encoding" ":" 1#transfer-coding
2588   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2590<figure><artwork type="example"><![CDATA[
2591  Transfer-Encoding: chunked
2594   If multiple encodings have been applied to an entity, the transfer-codings
2595   MUST be listed in the order in which they were applied.
2596   Additional information about the encoding parameters MAY be provided
2597   by other entity-header fields not defined by this specification.
2600   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2601   header.
2605<section title="Upgrade" anchor="header.upgrade">
2606  <iref primary="true" item="Upgrade header"/>
2607  <iref primary="true" item="Headers" subitem="Upgrade"/>
2609   The Upgrade general-header allows the client to specify what
2610   additional communication protocols it supports and would like to use
2611   if the server finds it appropriate to switch protocols. The server
2612   MUST use the Upgrade header field within a 101 (Switching Protocols)
2613   response to indicate which protocol(s) are being switched.
2615<figure><iref primary="true" item="Grammar" subitem="Upgrade"/><artwork type="abnf2616"><![CDATA[
2616  Upgrade        = "Upgrade" ":" 1#product
2619   For example,
2621<figure><artwork type="example"><![CDATA[
2622    Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2625   The Upgrade header field is intended to provide a simple mechanism
2626   for transition from HTTP/1.1 to some other, incompatible protocol. It
2627   does so by allowing the client to advertise its desire to use another
2628   protocol, such as a later version of HTTP with a higher major version
2629   number, even though the current request has been made using HTTP/1.1.
2630   This eases the difficult transition between incompatible protocols by
2631   allowing the client to initiate a request in the more commonly
2632   supported protocol while indicating to the server that it would like
2633   to use a "better" protocol if available (where "better" is determined
2634   by the server, possibly according to the nature of the method and/or
2635   resource being requested).
2638   The Upgrade header field only applies to switching application-layer
2639   protocols upon the existing transport-layer connection. Upgrade
2640   cannot be used to insist on a protocol change; its acceptance and use
2641   by the server is optional. The capabilities and nature of the
2642   application-layer communication after the protocol change is entirely
2643   dependent upon the new protocol chosen, although the first action
2644   after changing the protocol MUST be a response to the initial HTTP
2645   request containing the Upgrade header field.
2648   The Upgrade header field only applies to the immediate connection.
2649   Therefore, the upgrade keyword MUST be supplied within a Connection
2650   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2651   HTTP/1.1 message.
2654   The Upgrade header field cannot be used to indicate a switch to a
2655   protocol on a different connection. For that purpose, it is more
2656   appropriate to use a 301, 302, 303, or 305 redirection response.
2659   This specification only defines the protocol name "HTTP" for use by
2660   the family of Hypertext Transfer Protocols, as defined by the HTTP
2661   version rules of <xref target="http.version"/> and future updates to this
2662   specification. Any token can be used as a protocol name; however, it
2663   will only be useful if both the client and server associate the name
2664   with the same protocol.
2668<section title="Via" anchor="header.via">
2669  <iref primary="true" item="Via header"/>
2670  <iref primary="true" item="Headers" subitem="Via"/>
2672   The Via general-header field MUST be used by gateways and proxies to
2673   indicate the intermediate protocols and recipients between the user
2674   agent and the server on requests, and between the origin server and
2675   the client on responses. It is analogous to the "Received" field of
2676   <xref target="RFC2822"/> and is intended to be used for tracking message forwards,
2677   avoiding request loops, and identifying the protocol capabilities of
2678   all senders along the request/response chain.
2680<figure><iref primary="true" item="Grammar" subitem="Via"/><iref primary="true" item="Grammar" subitem="received-protocol"/><iref primary="true" item="Grammar" subitem="protocol-name"/><iref primary="true" item="Grammar" subitem="protocol-version"/><iref primary="true" item="Grammar" subitem="received-by"/><iref primary="true" item="Grammar" subitem="pseudonym"/><artwork type="abnf2616"><![CDATA[
2681  Via =  "Via" ":" 1#( received-protocol received-by [ comment ] )
2682  received-protocol = [ protocol-name "/" ] protocol-version
2683  protocol-name     = token
2684  protocol-version  = token
2685  received-by       = ( uri-host [ ":" port ] ) | pseudonym
2686  pseudonym         = token
2689   The received-protocol indicates the protocol version of the message
2690   received by the server or client along each segment of the
2691   request/response chain. The received-protocol version is appended to
2692   the Via field value when the message is forwarded so that information
2693   about the protocol capabilities of upstream applications remains
2694   visible to all recipients.
2697   The protocol-name is optional if and only if it would be "HTTP". The
2698   received-by field is normally the host and optional port number of a
2699   recipient server or client that subsequently forwarded the message.
2700   However, if the real host is considered to be sensitive information,
2701   it MAY be replaced by a pseudonym. If the port is not given, it MAY
2702   be assumed to be the default port of the received-protocol.
2705   Multiple Via field values represents each proxy or gateway that has
2706   forwarded the message. Each recipient MUST append its information
2707   such that the end result is ordered according to the sequence of
2708   forwarding applications.
2711   Comments MAY be used in the Via header field to identify the software
2712   of the recipient proxy or gateway, analogous to the User-Agent and
2713   Server header fields. However, all comments in the Via field are
2714   optional and MAY be removed by any recipient prior to forwarding the
2715   message.
2718   For example, a request message could be sent from an HTTP/1.0 user
2719   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2720   forward the request to a public proxy at, which completes
2721   the request by forwarding it to the origin server at
2722   The request received by would then have the following
2723   Via header field:
2725<figure><artwork type="example"><![CDATA[
2726    Via: 1.0 fred, 1.1 (Apache/1.1)
2729   Proxies and gateways used as a portal through a network firewall
2730   SHOULD NOT, by default, forward the names and ports of hosts within
2731   the firewall region. This information SHOULD only be propagated if
2732   explicitly enabled. If not enabled, the received-by host of any host
2733   behind the firewall SHOULD be replaced by an appropriate pseudonym
2734   for that host.
2737   For organizations that have strong privacy requirements for hiding
2738   internal structures, a proxy MAY combine an ordered subsequence of
2739   Via header field entries with identical received-protocol values into
2740   a single such entry. For example,
2742<figure><artwork type="example"><![CDATA[
2743    Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2746        could be collapsed to
2748<figure><artwork type="example"><![CDATA[
2749    Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2752   Applications SHOULD NOT  combine multiple entries unless they are all
2753   under the same organizational control and the hosts have already been
2754   replaced by pseudonyms. Applications MUST NOT combine entries which
2755   have different received-protocol values.
2761<section title="IANA Considerations" anchor="IANA.considerations">
2763   <cref>TBD.</cref>
2767<section title="Security Considerations" anchor="security.considerations">
2769   This section is meant to inform application developers, information
2770   providers, and users of the security limitations in HTTP/1.1 as
2771   described by this document. The discussion does not include
2772   definitive solutions to the problems revealed, though it does make
2773   some suggestions for reducing security risks.
2776<section title="Personal Information" anchor="personal.information">
2778   HTTP clients are often privy to large amounts of personal information
2779   (e.g. the user's name, location, mail address, passwords, encryption
2780   keys, etc.), and SHOULD be very careful to prevent unintentional
2781   leakage of this information.
2782   We very strongly recommend that a convenient interface be provided
2783   for the user to control dissemination of such information, and that
2784   designers and implementors be particularly careful in this area.
2785   History shows that errors in this area often create serious security
2786   and/or privacy problems and generate highly adverse publicity for the
2787   implementor's company.
2791<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2793   A server is in the position to save personal data about a user's
2794   requests which might identify their reading patterns or subjects of
2795   interest. This information is clearly confidential in nature and its
2796   handling can be constrained by law in certain countries. People using
2797   HTTP to provide data are responsible for ensuring that
2798   such material is not distributed without the permission of any
2799   individuals that are identifiable by the published results.
2803<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2805   Implementations of HTTP origin servers SHOULD be careful to restrict
2806   the documents returned by HTTP requests to be only those that were
2807   intended by the server administrators. If an HTTP server translates
2808   HTTP URIs directly into file system calls, the server MUST take
2809   special care not to serve files that were not intended to be
2810   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2811   other operating systems use ".." as a path component to indicate a
2812   directory level above the current one. On such a system, an HTTP
2813   server MUST disallow any such construct in the Request-URI if it
2814   would otherwise allow access to a resource outside those intended to
2815   be accessible via the HTTP server. Similarly, files intended for
2816   reference only internally to the server (such as access control
2817   files, configuration files, and script code) MUST be protected from
2818   inappropriate retrieval, since they might contain sensitive
2819   information. Experience has shown that minor bugs in such HTTP server
2820   implementations have turned into security risks.
2824<section title="DNS Spoofing" anchor="dns.spoofing">
2826   Clients using HTTP rely heavily on the Domain Name Service, and are
2827   thus generally prone to security attacks based on the deliberate
2828   mis-association of IP addresses and DNS names. Clients need to be
2829   cautious in assuming the continuing validity of an IP number/DNS name
2830   association.
2833   In particular, HTTP clients SHOULD rely on their name resolver for
2834   confirmation of an IP number/DNS name association, rather than
2835   caching the result of previous host name lookups. Many platforms
2836   already can cache host name lookups locally when appropriate, and
2837   they SHOULD be configured to do so. It is proper for these lookups to
2838   be cached, however, only when the TTL (Time To Live) information
2839   reported by the name server makes it likely that the cached
2840   information will remain useful.
2843   If HTTP clients cache the results of host name lookups in order to
2844   achieve a performance improvement, they MUST observe the TTL
2845   information reported by DNS.
2848   If HTTP clients do not observe this rule, they could be spoofed when
2849   a previously-accessed server's IP address changes. As network
2850   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
2851   possibility of this form of attack will grow. Observing this
2852   requirement thus reduces this potential security vulnerability.
2855   This requirement also improves the load-balancing behavior of clients
2856   for replicated servers using the same DNS name and reduces the
2857   likelihood of a user's experiencing failure in accessing sites which
2858   use that strategy.
2862<section title="Proxies and Caching" anchor="attack.proxies">
2864   By their very nature, HTTP proxies are men-in-the-middle, and
2865   represent an opportunity for man-in-the-middle attacks. Compromise of
2866   the systems on which the proxies run can result in serious security
2867   and privacy problems. Proxies have access to security-related
2868   information, personal information about individual users and
2869   organizations, and proprietary information belonging to users and
2870   content providers. A compromised proxy, or a proxy implemented or
2871   configured without regard to security and privacy considerations,
2872   might be used in the commission of a wide range of potential attacks.
2875   Proxy operators should protect the systems on which proxies run as
2876   they would protect any system that contains or transports sensitive
2877   information. In particular, log information gathered at proxies often
2878   contains highly sensitive personal information, and/or information
2879   about organizations. Log information should be carefully guarded, and
2880   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
2883   Proxy implementors should consider the privacy and security
2884   implications of their design and coding decisions, and of the
2885   configuration options they provide to proxy operators (especially the
2886   default configuration).
2889   Users of a proxy need to be aware that they are no trustworthier than
2890   the people who run the proxy; HTTP itself cannot solve this problem.
2893   The judicious use of cryptography, when appropriate, may suffice to
2894   protect against a broad range of security and privacy attacks. Such
2895   cryptography is beyond the scope of the HTTP/1.1 specification.
2899<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
2901   They exist. They are hard to defend against. Research continues.
2902   Beware.
2907<section title="Acknowledgments" anchor="ack">
2909   This specification makes heavy use of the augmented BNF and generic
2910   constructs defined by David H. Crocker for <xref target="RFC822ABNF"/>. Similarly, it
2911   reuses many of the definitions provided by Nathaniel Borenstein and
2912   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
2913   specification will help reduce past confusion over the relationship
2914   between HTTP and Internet mail message formats.
2917   HTTP has evolved considerably over the years. It has
2918   benefited from a large and active developer community--the many
2919   people who have participated on the www-talk mailing list--and it is
2920   that community which has been most responsible for the success of
2921   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
2922   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
2923   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
2924   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
2925   VanHeyningen deserve special recognition for their efforts in
2926   defining early aspects of the protocol.
2929   This document has benefited greatly from the comments of all those
2930   participating in the HTTP-WG. In addition to those already mentioned,
2931   the following individuals have contributed to this specification:
2934   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
2935   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
2936   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
2937   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
2938   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
2939   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
2940   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
2941   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
2942   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
2943   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
2944   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
2945   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
2946   Josh Cohen.
2949   Thanks to the "cave men" of Palo Alto. You know who you are.
2952   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
2953   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
2954   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
2955   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
2956   Larry Masinter for their help. And thanks go particularly to Jeff
2957   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
2960   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
2961   Frystyk implemented RFC 2068 early, and we wish to thank them for the
2962   discovery of many of the problems that this document attempts to
2963   rectify.
2970<references title="Normative References">
2972<reference anchor="ISO-8859-1">
2973  <front>
2974    <title>
2975     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
2976    </title>
2977    <author>
2978      <organization>International Organization for Standardization</organization>
2979    </author>
2980    <date year="1998"/>
2981  </front>
2982  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
2985<reference anchor="Part2">
2986  <front>
2987    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
2988    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2989      <organization abbrev="Day Software">Day Software</organization>
2990      <address><email></email></address>
2991    </author>
2992    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2993      <organization>One Laptop per Child</organization>
2994      <address><email></email></address>
2995    </author>
2996    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2997      <organization abbrev="HP">Hewlett-Packard Company</organization>
2998      <address><email></email></address>
2999    </author>
3000    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3001      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3002      <address><email></email></address>
3003    </author>
3004    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3005      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3006      <address><email></email></address>
3007    </author>
3008    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3009      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3010      <address><email></email></address>
3011    </author>
3012    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3013      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3014      <address><email></email></address>
3015    </author>
3016    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3017      <organization abbrev="W3C">World Wide Web Consortium</organization>
3018      <address><email></email></address>
3019    </author>
3020    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3021      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3022      <address><email></email></address>
3023    </author>
3024    <date month="February" year="2008"/>
3025  </front>
3026  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-02"/>
3030<reference anchor="Part3">
3031  <front>
3032    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3033    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3034      <organization abbrev="Day Software">Day Software</organization>
3035      <address><email></email></address>
3036    </author>
3037    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3038      <organization>One Laptop per Child</organization>
3039      <address><email></email></address>
3040    </author>
3041    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3042      <organization abbrev="HP">Hewlett-Packard Company</organization>
3043      <address><email></email></address>
3044    </author>
3045    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3046      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3047      <address><email></email></address>
3048    </author>
3049    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3050      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3051      <address><email></email></address>
3052    </author>
3053    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3054      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3055      <address><email></email></address>
3056    </author>
3057    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3058      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3059      <address><email></email></address>
3060    </author>
3061    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3062      <organization abbrev="W3C">World Wide Web Consortium</organization>
3063      <address><email></email></address>
3064    </author>
3065    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3066      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3067      <address><email></email></address>
3068    </author>
3069    <date month="February" year="2008"/>
3070  </front>
3071  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-02"/>
3075<reference anchor="Part5">
3076  <front>
3077    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3078    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3079      <organization abbrev="Day Software">Day Software</organization>
3080      <address><email></email></address>
3081    </author>
3082    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3083      <organization>One Laptop per Child</organization>
3084      <address><email></email></address>
3085    </author>
3086    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3087      <organization abbrev="HP">Hewlett-Packard Company</organization>
3088      <address><email></email></address>
3089    </author>
3090    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3091      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3092      <address><email></email></address>
3093    </author>
3094    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3095      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3096      <address><email></email></address>
3097    </author>
3098    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3099      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3100      <address><email></email></address>
3101    </author>
3102    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3103      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3104      <address><email></email></address>
3105    </author>
3106    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3107      <organization abbrev="W3C">World Wide Web Consortium</organization>
3108      <address><email></email></address>
3109    </author>
3110    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3111      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3112      <address><email></email></address>
3113    </author>
3114    <date month="February" year="2008"/>
3115  </front>
3116  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-02"/>
3120<reference anchor="Part6">
3121  <front>
3122    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3123    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3124      <organization abbrev="Day Software">Day Software</organization>
3125      <address><email></email></address>
3126    </author>
3127    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3128      <organization>One Laptop per Child</organization>
3129      <address><email></email></address>
3130    </author>
3131    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3132      <organization abbrev="HP">Hewlett-Packard Company</organization>
3133      <address><email></email></address>
3134    </author>
3135    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3136      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3137      <address><email></email></address>
3138    </author>
3139    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3140      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3141      <address><email></email></address>
3142    </author>
3143    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3144      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3145      <address><email></email></address>
3146    </author>
3147    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3148      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3149      <address><email></email></address>
3150    </author>
3151    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3152      <organization abbrev="W3C">World Wide Web Consortium</organization>
3153      <address><email></email></address>
3154    </author>
3155    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3156      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3157      <address><email></email></address>
3158    </author>
3159    <date month="February" year="2008"/>
3160  </front>
3161  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-02"/>
3165<reference anchor="RFC822ABNF">
3166  <front>
3167    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3168    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3169      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3170      <address><email>DCrocker@UDel-Relay</email></address>
3171    </author>
3172    <date month="August" day="13" year="1982"/>
3173  </front>
3174  <seriesInfo name="STD" value="11"/>
3175  <seriesInfo name="RFC" value="822"/>
3178<reference anchor="RFC2045">
3179  <front>
3180    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3181    <author initials="N." surname="Freed" fullname="Ned Freed">
3182      <organization>Innosoft International, Inc.</organization>
3183      <address><email></email></address>
3184    </author>
3185    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3186      <organization>First Virtual Holdings</organization>
3187      <address><email></email></address>
3188    </author>
3189    <date month="November" year="1996"/>
3190  </front>
3191  <seriesInfo name="RFC" value="2045"/>
3194<reference anchor="RFC2047">
3195  <front>
3196    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3197    <author initials="K." surname="Moore" fullname="Keith Moore">
3198      <organization>University of Tennessee</organization>
3199      <address><email></email></address>
3200    </author>
3201    <date month="November" year="1996"/>
3202  </front>
3203  <seriesInfo name="RFC" value="2047"/>
3206<reference anchor="RFC2119">
3207  <front>
3208    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3209    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3210      <organization>Harvard University</organization>
3211      <address><email></email></address>
3212    </author>
3213    <date month="March" year="1997"/>
3214  </front>
3215  <seriesInfo name="BCP" value="14"/>
3216  <seriesInfo name="RFC" value="2119"/>
3219<reference anchor="RFC2396">
3220  <front>
3221    <title abbrev="URI Generic Syntax">Uniform Resource Identifiers (URI): Generic Syntax</title>
3222    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3223      <organization abbrev="MIT/LCS">World Wide Web Consortium</organization>
3224      <address><email></email></address>
3225    </author>
3226    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3227      <organization abbrev="U.C. Irvine">Department of Information and Computer Science</organization>
3228      <address><email></email></address>
3229    </author>
3230    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3231      <organization abbrev="Xerox Corporation">Xerox PARC</organization>
3232      <address><email></email></address>
3233    </author>
3234    <date month="August" year="1998"/>
3235  </front>
3236  <seriesInfo name="RFC" value="2396"/>
3239<reference anchor="USASCII">
3240  <front>
3241    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3242    <author>
3243      <organization>American National Standards Institute</organization>
3244    </author>
3245    <date year="1986"/>
3246  </front>
3247  <seriesInfo name="ANSI" value="X3.4"/>
3252<references title="Informative References">
3254<reference anchor="Nie1997" target="">
3255  <front>
3256    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3257    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3258      <organization/>
3259    </author>
3260    <author initials="J." surname="Gettys" fullname="J. Gettys">
3261      <organization/>
3262    </author>
3263    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3264      <organization/>
3265    </author>
3266    <author initials="H." surname="Lie" fullname="H. Lie">
3267      <organization/>
3268    </author>
3269    <author initials="C." surname="Lilley" fullname="C. Lilley">
3270      <organization/>
3271    </author>
3272    <date year="1997" month="September"/>
3273  </front>
3274  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3277<reference anchor="Pad1995">
3278  <front>
3279    <title>Improving HTTP Latency</title>
3280    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3281      <organization/>
3282    </author>
3283    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3284      <organization/>
3285    </author>
3286    <date year="1995" month="December"/>
3287  </front>
3288  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3289  <annotation>
3290    Slightly revised version of paper in Proc. 2nd International WWW Conference '94: Mosaic and the Web, Oct. 1994,
3291    which is available at <eref target=""/>.
3292  </annotation>
3295<reference anchor="RFC822">
3296  <front>
3297    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3298    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3299      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3300      <address><email>DCrocker@UDel-Relay</email></address>
3301    </author>
3302    <date month="August" day="13" year="1982"/>
3303  </front>
3304  <seriesInfo name="STD" value="11"/>
3305  <seriesInfo name="RFC" value="822"/>
3308<reference anchor="RFC959">
3309  <front>
3310    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3311    <author initials="J." surname="Postel" fullname="J. Postel">
3312      <organization>Information Sciences Institute (ISI)</organization>
3313    </author>
3314    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3315      <organization/>
3316    </author>
3317    <date month="October" year="1985"/>
3318  </front>
3319  <seriesInfo name="STD" value="9"/>
3320  <seriesInfo name="RFC" value="959"/>
3323<reference anchor="RFC1123">
3324  <front>
3325    <title>Requirements for Internet Hosts - Application and Support</title>
3326    <author initials="R." surname="Braden" fullname="Robert Braden">
3327      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3328      <address><email>Braden@ISI.EDU</email></address>
3329    </author>
3330    <date month="October" year="1989"/>
3331  </front>
3332  <seriesInfo name="STD" value="3"/>
3333  <seriesInfo name="RFC" value="1123"/>
3336<reference anchor="RFC1305">
3337  <front>
3338    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3339    <author initials="D." surname="Mills" fullname="David L. Mills">
3340      <organization>University of Delaware, Electrical Engineering Department</organization>
3341      <address><email></email></address>
3342    </author>
3343    <date month="March" year="1992"/>
3344  </front>
3345  <seriesInfo name="RFC" value="1305"/>
3348<reference anchor="RFC1436">
3349  <front>
3350    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3351    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3352      <organization>University of Minnesota, Computer and Information Services</organization>
3353      <address><email></email></address>
3354    </author>
3355    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3356      <organization>University of Minnesota, Computer and Information Services</organization>
3357      <address><email></email></address>
3358    </author>
3359    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3360      <organization>University of Minnesota, Computer and Information Services</organization>
3361      <address><email></email></address>
3362    </author>
3363    <author initials="D." surname="Johnson" fullname="David Johnson">
3364      <organization>University of Minnesota, Computer and Information Services</organization>
3365      <address><email></email></address>
3366    </author>
3367    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3368      <organization>University of Minnesota, Computer and Information Services</organization>
3369      <address><email></email></address>
3370    </author>
3371    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3372      <organization>University of Minnesota, Computer and Information Services</organization>
3373      <address><email></email></address>
3374    </author>
3375    <date month="March" year="1993"/>
3376  </front>
3377  <seriesInfo name="RFC" value="1436"/>
3380<reference anchor="RFC1630">
3381  <front>
3382    <title abbrev="URIs in WWW">Universal Resource Identifiers in WWW: A Unifying Syntax for the Expression of Names and Addresses of Objects on the Network as used in the World-Wide Web</title>
3383    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3384      <organization>CERN, World-Wide Web project</organization>
3385      <address><email></email></address>
3386    </author>
3387    <date month="June" year="1994"/>
3388  </front>
3389  <seriesInfo name="RFC" value="1630"/>
3392<reference anchor="RFC1737">
3393  <front>
3394    <title abbrev="Requirements for Uniform Resource Names">Functional Requirements for Uniform Resource Names</title>
3395    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3396      <organization>Xerox Palo Alto Research Center</organization>
3397      <address><email></email></address>
3398    </author>
3399    <author initials="K." surname="Sollins" fullname="Karen Sollins">
3400      <organization>MIT Laboratory for Computer Science</organization>
3401      <address><email></email></address>
3402    </author>
3403    <date month="December" year="1994"/>
3404  </front>
3405  <seriesInfo name="RFC" value="1737"/>
3408<reference anchor="RFC1738">
3409  <front>
3410    <title>Uniform Resource Locators (URL)</title>
3411    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3412      <organization>CERN, World-Wide Web project</organization>
3413      <address><email></email></address>
3414    </author>
3415    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3416      <organization>Xerox PARC</organization>
3417      <address><email></email></address>
3418    </author>
3419    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3420      <organization>University of Minnesota, Computer and Information Services</organization>
3421      <address><email></email></address>
3422    </author>
3423    <date month="December" year="1994"/>
3424  </front>
3425  <seriesInfo name="RFC" value="1738"/>
3428<reference anchor="RFC1808">
3429  <front>
3430    <title>Relative Uniform Resource Locators</title>
3431    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3432      <organization>University of California Irvine, Department of Information and Computer Science</organization>
3433      <address><email></email></address>
3434    </author>
3435    <date month="June" year="1995"/>
3436  </front>
3437  <seriesInfo name="RFC" value="1808"/>
3440<reference anchor="RFC1900">
3441  <front>
3442    <title>Renumbering Needs Work</title>
3443    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3444      <organization>CERN, Computing and Networks Division</organization>
3445      <address><email></email></address>
3446    </author>
3447    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3448      <organization>cisco Systems</organization>
3449      <address><email></email></address>
3450    </author>
3451    <date month="February" year="1996"/>
3452  </front>
3453  <seriesInfo name="RFC" value="1900"/>
3456<reference anchor="RFC1945">
3457  <front>
3458    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3459    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3460      <organization>MIT, Laboratory for Computer Science</organization>
3461      <address><email></email></address>
3462    </author>
3463    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3464      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3465      <address><email></email></address>
3466    </author>
3467    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3468      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3469      <address><email></email></address>
3470    </author>
3471    <date month="May" year="1996"/>
3472  </front>
3473  <seriesInfo name="RFC" value="1945"/>
3476<reference anchor="RFC2068">
3477  <front>
3478    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3479    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3480      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3481      <address><email></email></address>
3482    </author>
3483    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3484      <organization>MIT Laboratory for Computer Science</organization>
3485      <address><email></email></address>
3486    </author>
3487    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3488      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3489      <address><email></email></address>
3490    </author>
3491    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3492      <organization>MIT Laboratory for Computer Science</organization>
3493      <address><email></email></address>
3494    </author>
3495    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3496      <organization>MIT Laboratory for Computer Science</organization>
3497      <address><email></email></address>
3498    </author>
3499    <date month="January" year="1997"/>
3500  </front>
3501  <seriesInfo name="RFC" value="2068"/>
3504<reference anchor="RFC2145">
3505  <front>
3506    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3507    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3508      <organization>Western Research Laboratory</organization>
3509      <address><email></email></address>
3510    </author>
3511    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3512      <organization>Department of Information and Computer Science</organization>
3513      <address><email></email></address>
3514    </author>
3515    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3516      <organization>MIT Laboratory for Computer Science</organization>
3517      <address><email></email></address>
3518    </author>
3519    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3520      <organization>W3 Consortium</organization>
3521      <address><email></email></address>
3522    </author>
3523    <date month="May" year="1997"/>
3524  </front>
3525  <seriesInfo name="RFC" value="2145"/>
3528<reference anchor="RFC2324">
3529  <front>
3530    <title abbrev="HTCPCP/1.0">Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)</title>
3531    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3532      <organization>Xerox Palo Alto Research Center</organization>
3533      <address><email></email></address>
3534    </author>
3535    <date month="April" day="1" year="1998"/>
3536  </front>
3537  <seriesInfo name="RFC" value="2324"/>
3540<reference anchor="RFC2616">
3541  <front>
3542    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3543    <author initials="R." surname="Fielding" fullname="R. Fielding">
3544      <organization>University of California, Irvine</organization>
3545      <address><email></email></address>
3546    </author>
3547    <author initials="J." surname="Gettys" fullname="J. Gettys">
3548      <organization>W3C</organization>
3549      <address><email></email></address>
3550    </author>
3551    <author initials="J." surname="Mogul" fullname="J. Mogul">
3552      <organization>Compaq Computer Corporation</organization>
3553      <address><email></email></address>
3554    </author>
3555    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3556      <organization>MIT Laboratory for Computer Science</organization>
3557      <address><email></email></address>
3558    </author>
3559    <author initials="L." surname="Masinter" fullname="L. Masinter">
3560      <organization>Xerox Corporation</organization>
3561      <address><email></email></address>
3562    </author>
3563    <author initials="P." surname="Leach" fullname="P. Leach">
3564      <organization>Microsoft Corporation</organization>
3565      <address><email></email></address>
3566    </author>
3567    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3568      <organization>W3C</organization>
3569      <address><email></email></address>
3570    </author>
3571    <date month="June" year="1999"/>
3572  </front>
3573  <seriesInfo name="RFC" value="2616"/>
3576<reference anchor="RFC2821">
3577  <front>
3578    <title>Simple Mail Transfer Protocol</title>
3579    <author initials="J." surname="Klensin" fullname="J. Klensin">
3580      <organization>AT&amp;T Laboratories</organization>
3581      <address><email></email></address>
3582    </author>
3583    <date year="2001" month="April"/>
3584  </front>
3585  <seriesInfo name="RFC" value="2821"/>
3588<reference anchor="RFC2822">
3589  <front>
3590    <title>Internet Message Format</title>
3591    <author initials="P." surname="Resnick" fullname="P. Resnick">
3592      <organization>QUALCOMM Incorporated</organization>
3593    </author>
3594    <date year="2001" month="April"/>
3595  </front>
3596  <seriesInfo name="RFC" value="2822"/>
3599<reference anchor="RFC3977">
3600  <front>
3601    <title>Network News Transfer Protocol (NNTP)</title>
3602    <author initials="C." surname="Feather" fullname="C. Feather">
3603      <organization>THUS plc</organization>
3604      <address><email></email></address>
3605    </author>
3606    <date year="2006" month="October"/>
3607  </front>
3608  <seriesInfo name="RFC" value="3977"/>
3611<reference anchor="RFC4288">
3612  <front>
3613    <title>Media Type Specifications and Registration Procedures</title>
3614    <author initials="N." surname="Freed" fullname="N. Freed">
3615      <organization>Sun Microsystems</organization>
3616      <address>
3617        <email></email>
3618      </address>
3619    </author>
3620    <author initials="J." surname="Klensin" fullname="J. Klensin">
3621      <organization/>
3622      <address>
3623        <email></email>
3624      </address>
3625    </author>
3626    <date year="2005" month="December"/>
3627  </front>
3628  <seriesInfo name="BCP" value="13"/>
3629  <seriesInfo name="RFC" value="4288"/>
3632<reference anchor="Spe" target="">
3633  <front>
3634  <title>Analysis of HTTP Performance Problems</title>
3635  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3636    <organization/>
3637  </author>
3638  <date/>
3639  </front>
3642<reference anchor="Tou1998" target="">
3643  <front>
3644  <title>Analysis of HTTP Performance</title>
3645  <author initials="J." surname="Touch" fullname="Joe Touch">
3646    <organization>USC/Information Sciences Institute</organization>
3647    <address><email></email></address>
3648  </author>
3649  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3650    <organization>USC/Information Sciences Institute</organization>
3651    <address><email></email></address>
3652  </author>
3653  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3654    <organization>USC/Information Sciences Institute</organization>
3655    <address><email></email></address>
3656  </author>
3657  <date year="1998" month="Aug"/>
3658  </front>
3659  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3660  <annotation>(original report dated Aug. 1996)</annotation>
3663<reference anchor="WAIS">
3664  <front>
3665    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3666    <author initials="F." surname="Davis" fullname="F. Davis">
3667      <organization>Thinking Machines Corporation</organization>
3668    </author>
3669    <author initials="B." surname="Kahle" fullname="B. Kahle">
3670      <organization>Thinking Machines Corporation</organization>
3671    </author>
3672    <author initials="H." surname="Morris" fullname="H. Morris">
3673      <organization>Thinking Machines Corporation</organization>
3674    </author>
3675    <author initials="J." surname="Salem" fullname="J. Salem">
3676      <organization>Thinking Machines Corporation</organization>
3677    </author>
3678    <author initials="T." surname="Shen" fullname="T. Shen">
3679      <organization>Thinking Machines Corporation</organization>
3680    </author>
3681    <author initials="R." surname="Wang" fullname="R. Wang">
3682      <organization>Thinking Machines Corporation</organization>
3683    </author>
3684    <author initials="J." surname="Sui" fullname="J. Sui">
3685      <organization>Thinking Machines Corporation</organization>
3686    </author>
3687    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3688      <organization>Thinking Machines Corporation</organization>
3689    </author>
3690    <date month="April" year="1990"/>
3691  </front>
3692  <seriesInfo name="Thinking Machines Corporation" value=""/>
3698<section title="Internet Media Types" anchor="">
3700   In addition to defining HTTP/1.1, this document serves
3701   as the specification for the Internet media type "message/http" and
3702   "application/http". The following is to be registered with IANA <xref target="RFC4288"/>.
3704<section title="Internet Media Type message/http" anchor="">
3705<iref item="Media Type" subitem="message/http" primary="true"/>
3706<iref item="message/http Media Type" primary="true"/>
3708   The message/http type can be used to enclose a single HTTP request or
3709   response message, provided that it obeys the MIME restrictions for all
3710   "message" types regarding line length and encodings.
3713  <list style="hanging">
3714    <t hangText="Type name:">
3715      message
3716    </t>
3717    <t hangText="Subtype name:">
3718      http
3719    </t>
3720    <t hangText="Required parameters:">
3721      none
3722    </t>
3723    <t hangText="Optional parameters:">
3724      version, msgtype
3725      <list style="hanging">
3726        <t hangText="version:">
3727          The HTTP-Version number of the enclosed message
3728          (e.g., "1.1"). If not present, the version can be
3729          determined from the first line of the body.
3730        </t>
3731        <t hangText="msgtype:">
3732          The message type -- "request" or "response". If not
3733          present, the type can be determined from the first
3734          line of the body.
3735        </t>
3736      </list>
3737    </t>
3738    <t hangText="Encoding considerations:">
3739      only "7bit", "8bit", or "binary" are permitted
3740    </t>
3741    <t hangText="Security considerations:">
3742      none
3743    </t>
3744    <t hangText="Interoperability considerations:">
3745      none
3746    </t>
3747    <t hangText="Published specification:">
3748      This specification (see <xref target=""/>).
3749    </t>
3750    <t hangText="Applications that use this media type:">
3751    </t>
3752    <t hangText="Additional information:">
3753      <list style="hanging">
3754        <t hangText="Magic number(s):">none</t>
3755        <t hangText="File extension(s):">none</t>
3756        <t hangText="Macintosh file type code(s):">none</t>
3757      </list>
3758    </t>
3759    <t hangText="Person and email address to contact for further information:">
3760      See Authors Section.
3761    </t>
3762                <t hangText="Intended usage:">
3763                  COMMON
3764    </t>
3765                <t hangText="Restrictions on usage:">
3766                  none
3767    </t>
3768    <t hangText="Author/Change controller:">
3769      IESG
3770    </t>
3771  </list>
3774<section title="Internet Media Type application/http" anchor="">
3775<iref item="Media Type" subitem="application/http" primary="true"/>
3776<iref item="application/http Media Type" primary="true"/>
3778   The application/http type can be used to enclose a pipeline of one or more
3779   HTTP request or response messages (not intermixed).
3782  <list style="hanging">
3783    <t hangText="Type name:">
3784      application
3785    </t>
3786    <t hangText="Subtype name:">
3787      http
3788    </t>
3789    <t hangText="Required parameters:">
3790      none
3791    </t>
3792    <t hangText="Optional parameters:">
3793      version, msgtype
3794      <list style="hanging">
3795        <t hangText="version:">
3796          The HTTP-Version number of the enclosed messages
3797          (e.g., "1.1"). If not present, the version can be
3798          determined from the first line of the body.
3799        </t>
3800        <t hangText="msgtype:">
3801          The message type -- "request" or "response". If not
3802          present, the type can be determined from the first
3803          line of the body.
3804        </t>
3805      </list>
3806    </t>
3807    <t hangText="Encoding considerations:">
3808      HTTP messages enclosed by this type
3809      are in "binary" format; use of an appropriate
3810      Content-Transfer-Encoding is required when
3811      transmitted via E-mail.
3812    </t>
3813    <t hangText="Security considerations:">
3814      none
3815    </t>
3816    <t hangText="Interoperability considerations:">
3817      none
3818    </t>
3819    <t hangText="Published specification:">
3820      This specification (see <xref target=""/>).
3821    </t>
3822    <t hangText="Applications that use this media type:">
3823    </t>
3824    <t hangText="Additional information:">
3825      <list style="hanging">
3826        <t hangText="Magic number(s):">none</t>
3827        <t hangText="File extension(s):">none</t>
3828        <t hangText="Macintosh file type code(s):">none</t>
3829      </list>
3830    </t>
3831    <t hangText="Person and email address to contact for further information:">
3832      See Authors Section.
3833    </t>
3834                <t hangText="Intended usage:">
3835                  COMMON
3836    </t>
3837                <t hangText="Restrictions on usage:">
3838                  none
3839    </t>
3840    <t hangText="Author/Change controller:">
3841      IESG
3842    </t>
3843  </list>
3848<section title="Tolerant Applications" anchor="tolerant.applications">
3850   Although this document specifies the requirements for the generation
3851   of HTTP/1.1 messages, not all applications will be correct in their
3852   implementation. We therefore recommend that operational applications
3853   be tolerant of deviations whenever those deviations can be
3854   interpreted unambiguously.
3857   Clients SHOULD be tolerant in parsing the Status-Line and servers
3858   tolerant when parsing the Request-Line. In particular, they SHOULD
3859   accept any amount of SP or HTAB characters between fields, even though
3860   only a single SP is required.
3863   The line terminator for message-header fields is the sequence CRLF.
3864   However, we recommend that applications, when parsing such headers,
3865   recognize a single LF as a line terminator and ignore the leading CR.
3868   The character set of an entity-body SHOULD be labeled as the lowest
3869   common denominator of the character codes used within that body, with
3870   the exception that not labeling the entity is preferred over labeling
3871   the entity with the labels US-ASCII or ISO-8859-1. See <xref target="Part3"/>.
3874   Additional rules for requirements on parsing and encoding of dates
3875   and other potential problems with date encodings include:
3878  <list style="symbols">
3879     <t>HTTP/1.1 clients and caches SHOULD assume that an RFC-850 date
3880        which appears to be more than 50 years in the future is in fact
3881        in the past (this helps solve the "year 2000" problem).</t>
3883     <t>An HTTP/1.1 implementation MAY internally represent a parsed
3884        Expires date as earlier than the proper value, but MUST NOT
3885        internally represent a parsed Expires date as later than the
3886        proper value.</t>
3888     <t>All expiration-related calculations MUST be done in GMT. The
3889        local time zone MUST NOT influence the calculation or comparison
3890        of an age or expiration time.</t>
3892     <t>If an HTTP header incorrectly carries a date value with a time
3893        zone other than GMT, it MUST be converted into GMT using the
3894        most conservative possible conversion.</t>
3895  </list>
3899<section title="Conversion of Date Formats" anchor="">
3901   HTTP/1.1 uses a restricted set of date formats (<xref target=""/>) to
3902   simplify the process of date comparison. Proxies and gateways from
3903   other protocols SHOULD ensure that any Date header field present in a
3904   message conforms to one of the HTTP/1.1 formats and rewrite the date
3905   if necessary.
3909<section title="Compatibility with Previous Versions" anchor="compatibility">
3911   It is beyond the scope of a protocol specification to mandate
3912   compliance with previous versions. HTTP/1.1 was deliberately
3913   designed, however, to make supporting previous versions easy. It is
3914   worth noting that, at the time of composing this specification
3915   (1996), we would expect commercial HTTP/1.1 servers to:
3916  <list style="symbols">
3917     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3918        1.1 requests;</t>
3920     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3921        1.1;</t>
3923     <t>respond appropriately with a message in the same major version
3924        used by the client.</t>
3925  </list>
3928   And we would expect HTTP/1.1 clients to:
3929  <list style="symbols">
3930     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3931        responses;</t>
3933     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3934        1.1.</t>
3935  </list>
3938   For most implementations of HTTP/1.0, each connection is established
3939   by the client prior to the request and closed by the server after
3940   sending the response. Some implementations implement the Keep-Alive
3941   version of persistent connections described in Section 19.7.1 of <xref target="RFC2068"/>.
3944<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3946   This section summarizes major differences between versions HTTP/1.0
3947   and HTTP/1.1.
3950<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
3952   The requirements that clients and servers support the Host request-header,
3953   report an error if the Host request-header (<xref target=""/>) is
3954   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-uri"/>)
3955   are among the most important changes defined by this
3956   specification.
3959   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3960   addresses and servers; there was no other established mechanism for
3961   distinguishing the intended server of a request than the IP address
3962   to which that request was directed. The changes outlined above will
3963   allow the Internet, once older HTTP clients are no longer common, to
3964   support multiple Web sites from a single IP address, greatly
3965   simplifying large operational Web servers, where allocation of many
3966   IP addresses to a single host has created serious problems. The
3967   Internet will also be able to recover the IP addresses that have been
3968   allocated for the sole purpose of allowing special-purpose domain
3969   names to be used in root-level HTTP URLs. Given the rate of growth of
3970   the Web, and the number of servers already deployed, it is extremely
3971   important that all implementations of HTTP (including updates to
3972   existing HTTP/1.0 applications) correctly implement these
3973   requirements:
3974  <list style="symbols">
3975     <t>Both clients and servers MUST support the Host request-header.</t>
3977     <t>A client that sends an HTTP/1.1 request MUST send a Host header.</t>
3979     <t>Servers MUST report a 400 (Bad Request) error if an HTTP/1.1
3980        request does not include a Host request-header.</t>
3982     <t>Servers MUST accept absolute URIs.</t>
3983  </list>
3988<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
3990   Some clients and servers might wish to be compatible with some
3991   previous implementations of persistent connections in HTTP/1.0
3992   clients and servers. Persistent connections in HTTP/1.0 are
3993   explicitly negotiated as they are not the default behavior. HTTP/1.0
3994   experimental implementations of persistent connections are faulty,
3995   and the new facilities in HTTP/1.1 are designed to rectify these
3996   problems. The problem was that some existing 1.0 clients may be
3997   sending Keep-Alive to a proxy server that doesn't understand
3998   Connection, which would then erroneously forward it to the next
3999   inbound server, which would establish the Keep-Alive connection and
4000   result in a hung HTTP/1.0 proxy waiting for the close on the
4001   response. The result is that HTTP/1.0 clients must be prevented from
4002   using Keep-Alive when talking to proxies.
4005   However, talking to proxies is the most important use of persistent
4006   connections, so that prohibition is clearly unacceptable. Therefore,
4007   we need some other mechanism for indicating a persistent connection
4008   is desired, which is safe to use even when talking to an old proxy
4009   that ignores Connection. Persistent connections are the default for
4010   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4011   declaring non-persistence. See <xref target="header.connection"/>.
4014   The original HTTP/1.0 form of persistent connections (the Connection:
4015   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
4019<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4021   This specification has been carefully audited to correct and
4022   disambiguate key word usage; RFC 2068 had many problems in respect to
4023   the conventions laid out in <xref target="RFC2119"/>.
4026   Transfer-coding and message lengths all interact in ways that
4027   required fixing exactly when chunked encoding is used (to allow for
4028   transfer encoding that may not be self delimiting); it was important
4029   to straighten out exactly how message lengths are computed. (Sections
4030   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4031   <xref target="header.content-length" format="counter"/>,
4032   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4035   The use and interpretation of HTTP version numbers has been clarified
4036   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4037   version they support to deal with problems discovered in HTTP/1.0
4038   implementations (<xref target="http.version"/>)
4041   Transfer-coding had significant problems, particularly with
4042   interactions with chunked encoding. The solution is that transfer-codings
4043   become as full fledged as content-codings. This involves
4044   adding an IANA registry for transfer-codings (separate from content
4045   codings), a new header field (TE) and enabling trailer headers in the
4046   future. Transfer encoding is a major performance benefit, so it was
4047   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4048   interoperability problem that could have occurred due to interactions
4049   between authentication trailers, chunked encoding and HTTP/1.0
4050   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4051   and <xref target="header.te" format="counter"/>)
4055<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4057  The CHAR rule does not allow the NUL character anymore (this affects
4058  the comment and quoted-string rules).
4059  (<xref target="basic.rules"/>)
4062  Clarify that HTTP-Version is case sensitive.
4063  (<xref target="http.version"/>)
4066  Remove reference to non-existant identity transfer-coding value tokens.
4067  (Sections <xref format="counter" target="transfer.codings"/> and
4068  <xref format="counter" target="message.length"/>)
4071  Clarification that the chunk length does not include
4072  the count of the octets in the chunk header and trailer.
4073  (<xref target="chunked.transfer.encoding"/>)
4076  Fix BNF to add query, as the abs_path production in
4077  Section 3 of <xref target="RFC2396"/> doesn't define it.
4078  (<xref target="request-uri"/>)
4081  Clarify exactly when close connection options must be sent.
4082  (<xref target="header.connection"/>)
4087<section title="Change Log (to be removed by RFC Editor before publication)">
4089<section title="Since RFC2616">
4091  Extracted relevant partitions from <xref target="RFC2616"/>.
4095<section title="Since draft-ietf-httpbis-p1-messaging-00">
4097  Closed issues:
4098  <list style="symbols">
4099    <t>
4100      <eref target=""/>:
4101      "HTTP Version should be case sensitive"
4102      (<eref target=""/>)
4103    </t>
4104    <t>
4105      <eref target=""/>:
4106      "'unsafe' characters"
4107      (<eref target=""/>)
4108    </t>
4109    <t>
4110      <eref target=""/>:
4111      "Chunk Size Definition"
4112      (<eref target=""/>)
4113    </t>
4114    <t>
4115      <eref target=""/>:
4116      "Message Length"
4117      (<eref target=""/>)
4118    </t>
4119    <t>
4120      <eref target=""/>:
4121      "Media Type Registrations"
4122      (<eref target=""/>)
4123    </t>
4124    <t>
4125      <eref target=""/>:
4126      "URI includes query"
4127      (<eref target=""/>)
4128    </t>
4129    <t>
4130      <eref target=""/>:
4131      "No close on 1xx responses"
4132      (<eref target=""/>)
4133    </t>
4134    <t>
4135      <eref target=""/>:
4136      "Remove 'identity' token references"
4137      (<eref target=""/>)
4138    </t>
4139    <t>
4140      <eref target=""/>:
4141      "Import query BNF"
4142    </t>
4143    <t>
4144      <eref target=""/>:
4145      "qdtext BNF"
4146    </t>
4147    <t>
4148      <eref target=""/>:
4149      "Normative and Informative references"
4150    </t>
4151    <t>
4152      <eref target=""/>:
4153      "RFC2606 Compliance"
4154    </t>
4155    <t>
4156      <eref target=""/>:
4157      "RFC977 reference"
4158    </t>
4159    <t>
4160      <eref target=""/>:
4161      "RFC1700 references"
4162    </t>
4163    <t>
4164      <eref target=""/>:
4165      "inconsistency in date format explanation"
4166    </t>
4167    <t>
4168      <eref target=""/>:
4169      "Date reference typo"
4170    </t>
4171    <t>
4172      <eref target=""/>:
4173      "Informative references"
4174    </t>
4175    <t>
4176      <eref target=""/>:
4177      "ISO-8859-1 Reference"
4178    </t>
4179    <t>
4180      <eref target=""/>:
4181      "Normative up-to-date references"
4182    </t>
4183  </list>
4186  Other changes:
4187  <list style="symbols">
4188    <t>
4189      Update media type registrations to use RFC4288 template.
4190    </t>
4191    <t>
4192      Use names of RFC4234 core rules DQUOTE and HTAB,
4193      fix broken ABNF for chunk-data
4194      (work in progress on <eref target=""/>)
4195    </t>
4196  </list>
4200<section title="Since draft-ietf-httpbis-p1-messaging-01">
4202  Closed issues:
4203  <list style="symbols">
4204    <t>
4205      <eref target=""/>:
4206      "Bodies on GET (and other) requests"
4207    </t>
4208    <t>
4209      <eref target=""/>:
4210      "Updating to RFC4288"
4211    </t>
4212    <t>
4213      <eref target=""/>:
4214      "Status Code and Reason Phrase"
4215    </t>
4216    <t>
4217      <eref target=""/>:
4218      "rel_path not used"
4219    </t>
4220  </list>
4223  Ongoing work on ABNF conversion (<eref target=""/>):
4224  <list style="symbols">
4225    <t>
4226      Get rid of duplicate BNF rule names ("host" -&gt; "uri-host", "trailer" -&gt;
4227      "trailer-part").
4228    </t>
4229    <t>
4230      Avoid underscore character in rule names ("http_URL" -&gt;
4231      "http-URL", "abs_path" -&gt; "path-absolute").
4232    </t>
4233    <t>
4234      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4235      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4236      have to be updated when switching over to RFC3986.
4237    </t>
4238    <t>
4239      Synchronize core rules with RFC5234 (this includes a change to CHAR
4240      which now excludes NUL).
4241    </t>
4242    <t>
4243      Get rid of prose rules that span multiple lines.
4244    </t>
4245    <t>
4246      Get rid of unused rules LOALPHA and UPALPHA.
4247    </t>
4248    <t>
4249      Move "Product Tokens" section (back) into Part 1, as "token" is used
4250      in the definition of the Upgrade header.
4251    </t>
4252    <t>
4253      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4254    </t>
4255    <t>
4256      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4257    </t>
4258  </list>
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